TWENTIETH   CENTURY  TEXT-BOOKS 


A.   F.   NIGHTINGALE,    PH.D.,   LL.D. 

FORMERLY    SUPERINTENDENT    OF    HIGH    SCHOOLS,    CHICAGC 


TWENTIETH    CENTURY    TEXT-BOOKS 

ANIMAL    FORMS 

A  TEXT-BOOK  OF  ZOOLOGY 


BY 

DAVID  S.  JORDAN,  M.  S.,  M.  D.,  PH.  D.,  LL.  D 

PRESIDENT    OF    LELAND    STANFORD    JUNIOR    UNIVERSITY 
AND 

HAROLD  HEATH,   PH.  D. 

PROFESSOR    IN    LELAND    STANFORD    JUNIOR    UNIVERSITY 


NEW    YORK 

D.    APPLETON     AND    COMPANY 
1902 


COPYRIGHT,  1902 
BY   D.    APPLETON   AND   COMPANY 


Published  Mny,  1902 


PKEFACE 


THE  present  volume  is  designed  to  meet  the  needs  of 
the  beginning  student  of  zoology.  Accordingly,  technical 
and  scientific  names  have  been  avoided  as  far  as  possible, 
and  those  used  are  fully  explained  in  the  text  or  elsewhere. 
The  opening  chapters  deal  with  the  characteristics  of  living 
things,  and,  in  contrasting  animals  and  plants,  attempt  to 
bring  into  relief  the  distinguishing  marks  of  all  animals. 
Then  follows  a  discussion  of  the  cell  and  protoplasm,  pre- 
paring the  way  for  the  examination  of  a  series  of  animals 
representative  of  each  of  the  great  groups,  from  the  sim- 
plest to  the  most  complex.  These  are  considered  from  the 
view-point  of  structure ;  but  considerable  attention  is  also 
paid  to  the  functions  of  their  parts,  to  their  habits  and  life- 
history,  so  that  while  the  representatives  examined  are,  for 
the  sake  of  simplicity,  relatively  few  in  number,  they  are,  it 
is  believed,  thoroughly  typical.  Hence,  with  a  knowledge 
of  the  facts  presented,  the  student  should  have  a  broad 
view  of  the  animal  kingdom,  and  a  foundation  on  which  to 
base  future  study  and  observation.  It  is  perhaps  unneces- 
sary to  add  that  from  the  study  of  books  alone  no  one  can 
really  make  such  knowledge  his  own.  A  personal  acquaint- 
ance with  even  a  few  animals  in  their  native  haunts,  and 
an  understanding  of  the  structure  and  the  function  of  their 


vi  ANIMAL  FORMS 

parts  gained  from  dissection  and  experiment,  is  essential  to 
a  full  comprehension  of  what  the  student  learns  from  text- 
book and  teacher. 

The  greater  number  of  illustrations  are  new,  and  have 
been  drawn  or  photographed  from  living  or  preserved  ma- 
terial. When  not  otherwise  accredited,  the  drawings  have 
been  made  by  Miss  Mary  H.  AVellman  and  J.  Carter  Beard, 
to  whom  the  authors  extend  their  sincere  thanks.  Our 
obligations  are  also  due  to  Mr.  Walter  K.  Fisher,  who  has 
made  the  drawings  of  the  vertebrate  dissections ;  to  Messrs. 
A.  L.  Melander  and  C.  T.  Brues,  of  Chicago,  111.  ;  Mr.  Wm. 
H.  Fisher,  of  Baltimore,  Md. ;  Kev.  H.  K.  Job,  of  Kent, 
Conn. ;  Mr.  Wm.  Graham,  of  Pasadena,  Cal. ;  and  Dr.  K.  W. 
Shufeldt,  of  New  York  city,  for  numerous  photographs. 

DAVID  STABB  JOBDAN, 
HABOLD  HEATH. 


CONTENTS 


CHAPTER 

PAGE 
1 

II  —  THE   CELL   AND   PROTOPLASM         .                                  . 

7 

III.—  THE  PROTOZOA    .        .... 
IV.—  THE  SPONGES       .        .        .               •.  .      . 

V.  —  THE    Co3LENTERATES                .           -.      '      . 

.      11 
.       19 
29 

V>VI.—  THE  WORMS        .        .     "  
VII.  —  ANIMALS  OF  UNCERTAIN  RELATIONSHIPS^". 

\yni.—  MOLLUSKS    

IX.  —  ARTHROPODS.    CLASS  CRUSTACEA      .... 
X.—  ARTHROPODS.    CLASS  INSECTS   .    '    ,  •       . 
XL  —  ARTHROPODS.    CLASS  ARACHNID  A      .... 

XII        ECHINODERMS 

.      44  y 

.      66 

.      93 
.     114 
.     133 
140 

XIII.  —  THE  CHORDATES  
XIV.—  THE  FISHES^.     

'N^xXV.  —  THE   AMPHIBIANS     "^  .           .                      .... 

.     151 

.     154 

\_XVI.—  THE  REPTILES  s.        .'       . 
.:VIL—  THE  BIRDSX"       
-XVIIL—  THE  MAMMALS  /     

vii 

1 

.     184v/ 
.     201 
.    2Q5^ 

ANIMAL   FORMS 


CHAPTEE  I 

INTRODUCTION 

tlBfeT) 

1.  Divisions  of  the  subject. — Biology  is  the  science  which 

treats  of  living  things  in  all  their  relations.  It  is  sub- 
divided into  Zoology,  the  science  which  deals  with  animals, 
and  Botany,  which  is  concerned  with  plants.  The  field 
covered  by  each  of  these  branches  is  very  extensive. 
Within  the  scope  of  zoology  are  included  all  subjects  bear- 
ing on  the  form  and  structure  of  animals,  on  their  devel- 
opment, and  on  their  activities,  including  the  consideration 
of  their  habits  and  the  wider  problems  of  their  distribution 
and  their  relations  to  one  another. 

These  various  subjects  are  often  conveniently  grouped 
under  three  heads :  Morphology,  which  treats  of  the  form 
and  structure  or  the  anatomy  of  organisms ;  Physiology, 
which  considers  their  activities ;  and  Ecology,  which  in- 
cludes their  relations  one  to  another  and  to  their  surround- 
ings. All  the  phases  of  plant  or  animal  existence  may  be 
considered  under  one  or  another  of  these  three  divisions. 

2.  The  difference  between  animals  and  plants.— Generally 
speaking,  we  have  little  difficulty  in  seeing  that  the  objects 
about  us  are  either  living  or  lifeless  ;  but  the  boundary  line 
between  the  two  great  divisions  of  living  things,  the  animals 
and  plants,  can  not  always  be  so  clearly  drawn.     This  is  es- 
pecially true  of  the  simpler  forms  of  life  which  frequently 
combine  both  animal  and  plant  characteristics ;  but  in  the 

1 


2  ANIMAL  FORMS 

greater  number  of  more  highly  developed  species  the  line 
of  separation  is  clearly  marked.  It  is  very  easy,  for  example, 
to  distinguish  the  oak-tree  or  the  rose  from  a  horse  or  a 
butterfly,  and,  as  we  shall  see,  the  differences  are  not  based 
merely  on  outward  appearance. 

In  the  oak-tree,  for  example,  the  roots  reaching  down 
into  the  earth,  with  the  branches  and  leaves  spreading  out 
into  the  air  and  sunlight,  are  admirably  fitted  for  taking  up 
the  food,  which  consists  of  very  simple  materials,  less  com- 
plex than  those  forming  the  diet  of  an  animal.  This 
permits  a  continuous  existence  in  one  place,  and  accord- 
ingly we  note  the  entire  absence  of  locomotion  and  the  or- 
gans controlling  it,  which  form  so  conspicuous  a  part  of  the 
body  of  an  animal.  Also  in  the  production  of  flowers  and 
seeds,  and  in  the  growth  of  the  seed  into  the  tree,  we  detect 
many  characteristics  peculiar  to  plants. 

3.  Characteristics  of  an  animal— On  the  other  hand,  the 
squirrel,  for  example,  or  any  other  animal,  is  unable  to  sub- 
sist on  water,  air,  and  elements  from  the  soil.  These  crea- 
tures demand  the  highly  diversified  materials  found  in  the 
bodies  of  plants  and  of  animals.  Such  being  the  case,  they 
do  not  remain  anchored  to  one  spot  (except  in  a  relatively 
few  cases),  but  are  compelled  to  lead  an  active  existence. 
The  power  of  voluntary  movement,  or  movement  in  response 
to  internal  impulse,  is  thus  the  first  and  one  of  the  most 
striking  peculiarities  of  animals. 

In  the  second  place,  the  food  of  plants  enters  the  body 
in  a  soluble  condition  and  is  readily  transferred  to  the  or- 
gans requiring  it.  While  in  the  animals,  the  nutritive  ma- 
terials pass  into  the  body  in  an  insoluble  state  and  de- 
mand a  varied  preliminary  treatment,  usually  within  a 
special  digestive  tube,  before  they  are  fit  to  be  absorbed. 
In  the  squirrel,  by  way  of  illustration,  the  food  is  first 
ground  to  a  pulp  by  the  action  of  the  teeth,  and,  moistened 
with  saliva,  is  swallowed  and  passed  into  the  stomach, 
where  it  is  subjected  to  the  solvent  action  of  the  gastric 


ANIMAL  FORMS 


juice.  From  the  stomach  it  is  made  to  enter  the  intestine, 
and  is  further  acted  upon  by  fluids  from  the  liver,  the 
pancreas,  and  the  glands  of  the 
intestines  themselves.  Thus 
treated  it  becomes  changed  from 
an  insoluble  state  into  a  fluid 
which  readily  penetrates  the 
coats  of  the  digestive  tract. 

Many  of  the  organs  of  the 
body  are  placed  at  a  considera- 
ble distance  from  the  food  as 
it  comes  through  the  coats  of 
the  stomach  and  intestine.  In 
order  to  supply  them  with  the 
necessary  nourishment  a  distrib- 
uting apparatus  is  required. 
This  is  the  office  performed  by 
the  circulatory  system,  for  as 
rapidly  as  the  food  penetrates 
the  walls  of  the  digestive  tract 
it  enters  the  blood,  and  by  the 
beating  of  the  heart  is  driven 
to  all  parts  of  the  body,  which 
are  thus  continually  kept  in  a 
state  of  repair.  The  blood  serves 
also  to  remove  waste  substances 
from  the  various  structures  or 
organs  of  the  animal  body  and 
to  transfer  them  to  the  kidneys, 
skin,  or  lungs,  which  effect  their 
removal  from  the  body. 

4.  Muscular  and  nervous  sys- 
tems.—Owing  to  the  fact  that 
animals,  as  a  rule,  are  compelled 
to  move  about  in  search  of  food,  we  find  two  highly  devel- 
oped systems,  the  muscular  and  nervous,  which  are  absent 


FIG.  2. — Diagram  of  heart  and  blood- 
vessels of  the  squirrel  or  other 
mammal,  a.o.,  aorta  ;  h,  vessels 
of  head  ;  l.a.,  left  auricle  ;  Lex., 
vessels  of  lower  extremities  ;  lg., 
lung ;  l.v.,  left  ventricle  ;  p.a., 
pulmonary  artery  ;  p.v.,  pulmo- 
nary vein  ;  r.a.,  right  auricle  ; 
r.v.,  right  ventricle  ;  v.,  vessels  of 
viscera.  Arteries  are  represented 
by  heavy  walls. 


INTRODUCTION  5 

in  the  plants.  The  first  of  these,  constituting  what  is  usu- 
ally known  as  the  lean  meat,  is  a  relatively  complex  system 
of  organs,  differing  widely  according  to  the  work  performed. 
In  the  higher  animals — the  squirrel,  for  example — there  are 
not  less  than  five  hundred  muscles,  which  are  under  the 
control  of  the  nervous  system. 

The  nervous  system  consists  of  the  brain  and  spinal 
cord,  which  in  the  squirrel  are  concealed  and  protected 


FIG.  3.— Skeleton  of  squirrel,  showing  its  relation  to  the  body. 

within  the  skull  and  back-bone.  From  them  many  nerves 
pass  outward  to  the  muscles,  and  as  many  pass  inward  from 
the  eye,  ear,  nose,  tongue,  or  skin.  By  the  action  of  these 
sense-organs  the  animal  determines  the  nature  of  its  sur- 
roundings, detects  its  food,  recognizes  the  presence  of  its 
enemies,  and  is  thus  able  to  direct  its  movements  to  the 
greatest  advantage. 

5.  Multiplication  of  animals.— The  organs  thus  far  con- 
sidered serve  to  perpetuate  the  animal  as  an  individual ; 
but  some  provision  must  also  be  made  for  the  continuance 
of  the  race.  In  the  economy  of  nature  each  animal  before 


6  ANIMAL   FORMS 

its  death  should  leave  offspring  to  take  the  place  of  the 
parent  when  it  falls  from  the  ranks.  This  is  effected  in 
various  ways.  In  some  of  the  simpler  animals  the  body 
may  divide  into  two  equal  parts,  each  of  which  becomes  a 
complete  individual.  In  other  cases  the  animal  detaches 
a  relatively  small  portion  of  its  body,  much  as  a  gardener 
cuts  a  slip  from  a  plant,  and  this  likewise  develops  into  a 
new  organism.  In  the  greater  number  of  animals,  very 
clearly  illustrated  by  the  birds,  eggs  are  produced  which 
under  favorable  conditions  develop  into  an  organism  resem- 
bling the  parents. 

6.  Summary. — Animals  are  thus  seen  to  lead  active,  busy 
lives,  collecting  food,  avoiding  enemies,  and  producing  and 
and  caring  for  their  young.  While  the  activities  of  all 
animals  are  directed  to  their  own  preservation  and  to  the 
multiplication  of  their  kind,  these  processes  are  carried  on 
in  the  most  diverse  ways.  The  manner  in  which  an  organ 
or  an  organism  is  made,  and  the  method  by  which  it  does 
its  work,  are  mutually  dependent  one  on  the  other.  As 
there  is  an  enormous  number  of  species  of  animals,  each 
differently  constructed,  there  is,  accordingly,  a  very  great 
variety  of  habits.  As  we  shall  see,  the  lower  forms  are 
remarkably  simple  in  their  construction,  and  their  mode  of 
existence  is  correspondingly  simple.  In  the  higher  types 
a  much  greater  complexity  exists,  and  their  activities  are 
more  varied  and  are  characterized  by  a  high  degree  of  elabo- 
ration. In  every  case,  the  animal,  whether  high  or  low,  is 
fitted  for  some  particular  haunt,  where  it  may  perform  its 
work  in  its  own  special  way  and  may  lead  a  successful  life 
of  its  own  characteristic  type. 


CHAPTER   II 

THE   CELL   AND   PROTOPLASM 

7.  Cells.— If  we  examine  very  carefully  the  different  parts 
of  a  squirrel  under  the  high  powers  of  the   microscope 
we  find  that  they  are  composed  of  a  multitude  of  small 
structures  which  bear  the  same  relations  to  the  various 
organs  that  bricks  or  stones  do  to  a  wall ;  and  if  the  inves- 
tigation were  continued  it  would  be  found  that  every  or- 
ganism is  composed  of  one  or  more  of  these  lesser  elements 
which  bear  the  name  of  cells.    In  size  they  vary  exceedingly, 
and  their  shapes  are  most  diverse,  but,  despite  these  differ- 
ences, it  will  be  seen  that  all  exhibit  a  certain  general  re- 
semblance one  to  the  other. 

8.  Shape  of  cells. — In  many  of   the   simpler  organisms 
the  component  cells  are  jelly-like  masses  of  a  more  or  less 
spherical  form,  but  as  we  ascend  the  scale  of  life  the  condi- 
tion of  affairs  becomes  much  more  complex.     In  the  squir- 
rel, for  example,  we  have  already  noted  the  presence  of 
various  organs  for  carrying  on  different  functions,  such  as 
those  of  digestion,  circulation,  and  respiration ;  and,  further, 
the  cells  composing  these  various  parts  have  been  modified 
in  accordance  with  the  duties  they  have  to  perform.     In 
the  muscles  the  cells  are  long  and  slender  (Fig.  4,  D) ; 
those  forming  the  nerves  and  conveying  sensations  to  and 
from  all  parts  of  the  body,  like  an  extensive  telegraph  sys- 
tem, are  excessively  delicate  and  thread-like ;  in  the  skin, 
and  lining  many  cavities  of  the  body,  where  the  cells  are 
united  into  extensive  sheets,  they  range  in  shape  from  high 
and  columnar  to  flat  and  scale-like  forms  (Fig.  4,  E,  F,  G). 

2  7 


8  ANIMAL  FORMS 

The  cells  of  the  blood  present  another  type  (Fig.  4,  B) ;  and 
so  we  might  pass  in  review  other  parts  of  the  body,  and  con- 
tinue our  studies  with  other  groups  of  animals,  always  find- 
ing new  forms  dependent  upon  the  part  they  play  in  the 
organism. 

9.  Size  of  cells.— Also  in  the  matter  of  size  the  greatest 
variations  exist.     Some  of  the  smallest  cells  measure  less 
than  one  micromillimeter  (j^f^o  °f  an  incn)  in  diameter. 
Over  five  hundred  million  such  bodies  could  be  readily 
stowed  away  into  a  hollow  sphere  the  size  of  the  letter  be- 
ginning this  sentence.     In  a  drop  of  human  blood  of  the 
same  size,  between  four  and  five  million  blood-cells  or  cor- 
puscles float.     And  from  this  extreme  all  sizes  exist  up  to 
those  with  a  diameter  of  2.5  or  5  c.m.  (one  or  two  inches), 
as  in  the  case  of  the  hen's  or  ostrich's  egg.     On  the  average 
a  cell  will  measure  between  .025  to  .031  m.m.  (TT5Vfr  and 
-g-J-o  of  an  inch)  in  diameter,  a  speck  probably  invisible  to 
the  unaided  eye.     While  the  size  and  external  appearance 
of  a  cell  are  seen  to  be  most  variable,  the  internal  structures 
are  found  to  show  a  striking  resemblance  throughout.     All 
are  constructed  upon  essentially  the  same  plan.     Differ- 
ences in  form  and  size  are  superficial,  and  in  passing  to  a 
more  careful  study  of  one  cell  we  gain  a  knowledge  of  the 
important  features  of  ali. 

10.  A  typical  cell.— Some  cell,  for  example  that  of  the 
liver  (Fig.  4,  A),  may  be  chosen  as  a  good  representative  of 
a  typical  cell.     To  the  naked  eye  it  is  barely  visible  as  a 
minute  speck ;  but  under  the  microscope  the  appearance  is 
that  of  so  much  white  of  egg,  an  almost  transparent  jelly- 
like  mass  bearing  upon  its  outer  surface  a  thin  structure- 
less membrane  that  serves  to  preserve  its  general  shape  and 
also  to  protect  the  delicate  cell  material  within.    The  com- 
parison of  the  latter  substance  to  egg  albumen  can  be  car- 
ried no  further  than  the  simple  physical  appearance,  for 
albumen  belongs  to  that  great  class  of  substances  which 
are  said  to  be  non-living  or  dead,  while  the  cell  material 


THE   CELL   AND   PROTOPLASM  9 

or  protoplasm,  as  it  is  termed,  is  a  living  substance.  We 
know  of  no  case  where  life  exists  apart  from  protoplasm, 
and  for  this  reason  the  latter  is  frequently  termed  the 
physical  basis  of  life. 

In  addition  to  the  features  already  described,  the  proto- 
plasm of  every  perfect  cell  is  modified  upon  the  interior  to 


FIG.  4.— Different  types  of  cells  composing  the  body  of  the  squirrel  or  other  highly 
developed  animal.  A,  liver-cell  ;  /,  food  materials  ;  n,  nucleus.  B,  blood-cell. 
C,  nerve-cell  with  small  part  of  its  fiber.  D,  muscle  fiber.  E,  cells  lining  the 
body  cavity.  F,  lining  of  the  windpipe.  G,  section  through  the  skin.  Highly 


form  a  well-defined  spherical  mass  known  as  the 
Other  structures  are  known  to  occur  in  the  typical  cell. 
Experiment  shows  that  the  nucleus  and  cell  protoplasm  are 
absolutely  indispensable,  whatever  their  size  and  shape,  and 


10  ANIMAL  FORMS 

therefore  we  are  at  present  justified  in  defining  the  cell  as 
a  small  mass  of  protoplasm  enclosing  a  nucleus. 

11.  Structure  of  protoplasm.— When  seen  under  a  glass 
of  moderate  power  protoplasm  gives  no  indication  of  any 
definite  structure,  and  even  with  the  highest  magnifica- 
tion it  presents  appearances  which  are  not  clearly  under- 
stood. According  to  the  commonly  accepted  view,  it  con- 
sists of  two  portions,  one,  the  firmer,  forming  an  excessively 
delicate  mesh  work  (Fig.  4,  A)  enclosing  in  its  cavities 
the  second  more  fluid  part.  Therefore,  when  highly  mag- 
nified, the  appearance  would  be  essentially  like  a  sponge 
fully  saturated  with  water ;  but  it  should  be  remembered 
that  in  the  protoplasm  the  sponge  work,  and  possibly  the 
fluid  part,  is  living,  and  that  both  are  transparent. 

There  are  reasons  for  thinking  that  the  structure  and 
the  composition  of  protoplasm  may  change  somewhat  under 
certain  circumstances.  It  certainly  is  not  everywhere  alike, 
for  that  of  one  animal  must  differ  from  that  of  another,  and 
different  parts,  such  as  the  liver  and  brain,  of  the  same  form 
must  be  unlike.  These  differences,  however,  are  minor 
when  compared  to  the  resemblances,  for,  as  we  shall  see, 
this  living  substance,  wherever  it  exists,  carries  on  the  pro- 
cesses of  waste,  repair,  growth,  sensation,  contraction,  and 
the  reproduction  of  its  kind. 


CHAPTER  III 

THE    PROTOZOA 

12.  Single-celled   and    many-celled    animals.— In  almost 
every  portion  of  the  globe  there  are  multitudes  of  animals 
whose  body  consists  of  but  a  single  cell ;  while  those  forms 
more  familiar  to  us,  and  usually  of  comparatively  large 
size  and  higher   development,   such   as   sponges,  insects, 
fishes,  birds,  and  man  himself,  are  composed  of  a  multitude 
of  cells.     For  this  reason  the  animal  kingdom  has  been 
divided  into  two  great  subdivisions,  the  Protozoa  including 
all  unicellular  forms  and  the  Metazoa  embracing  those  of 
many  cells. 

13.  Single-celled  animals. — The  division  of  the  Protozoa 
comprises  a  host  of  animals,  usually  of  microscopic  size, 
inhabiting  fresh  or  salt  water  or  damp  localities  on  land  in 
nearly  every  portion  of  the  globe.     The  greater  number 
wage  their  little,  though  fierce,  wars  on  one  another  with- 
out attracting  much  attention ;  others,  in  the  sharp  struggle, 
have  been  compelled  to  live  upon  or  within  the  bodies  of 
other  animals,  and  many  have  become  notorious  because  of 
the  diseases  they  produce  under  such  circumstances.     A 
few  are  in  large  measure  responsible  for  the  phosphores- 
cence of  the  sea ;  and  still  others  have  long  been  favorite 
objects  of  study  because  of  their  marvelous  beauty.   Adapted 
for  living  under  diverse  conditions,  the  bodily  form  differs 
greatly,  and  yet  all  conform  to  three  or  four  principal  types, 
of  which  we  may  gain  a  good  idea  from  the  study  of  a  few 
representative  forms. 

11 


12 


ANIMAL  FORMS 


14.  The  Amoeba. — Among  the  simplest  one-celled  ani- 
mals living  in  the  ooze  at  the  bottom  of  nearly  every  fresh- 
water stream  or  pond  is  the  Amoeba  (Fig.  5,  A),  whose  body 
is  barely  visible  to  the  unaided  eye.  Under  the  microscope 


FIG.  5.— A,  the  Amoeba,  highly  magnified,  showing  c.  r.,  pulsating  vacnole  ;  /,  food 
particle  ;  n,  nucleus.  The  arrows  show  the  direction  of  movement.  B,  shape  of 
same  individual  30  seconds  later.  C,  an  amoeba-like  animal  (Difflugia)  partially 
enclosed  in  a  shell.  D,  an  Amoeba  in  the  process  of  division.  E,  Gromia,  another 
shelled  protozoan  (after  SCHULZE). 

it  is  seen  to  consist  of  an  irregular,  jelly-like  mass  of  proto- 
plasm totally  destitute  of  a  cell  wall.  Unlike  those  animals 
with  which  we  are  familiar,  the  body  constantly  changes  its 
shape.  A  rounded  bud-like  projection  will  be  seen  to  appear 
on  one  side  of  the  body  and  the  protoplasm  of  adjacent 
regions  flows  into  it,  thereby  increasing  its  extent.  Similar 
projections  at  the  opposite  end  of  the  cell  are  withdrawn, 
and  their  substance  may  flow  into  the  newly  formed  lobe, 
which  gradually  swells  in  size  and  pushes  forward.  Thus, 
by  constantly  advancing  the  front  part  of  the  body  and 


THE   PROTOZOA  13 

,  retracting  the  hinder  portion,  the  cell  glides  or  flows  along 
from  place  to  place. 

Upon  meeting  with  any  of  the  smaller  organisms  upon 
which  it  lives,  projections  from  the  body  are  put  out  which 
gradually  flow  around  the  prey  and  it  becomes  pressed  into 
the  interior  of  the  cell.  The  process  is  not  unlike  pushing 
a  grain  of  sand  into  a  bit  of  jelly.  There  is  no  mouth. 
Any  point  on  the  surface  serves  for  the  reception  of  food. 
Oxygen  gas  also  is  taken  into  the  body  all  over  the  surface, 
and  wastes  and  indigestible  material  are  cast  out  at  any 
point.  Nothing  exists  in  these  simple  forms  comparable  to 
the  complex  systems  of  organs  that  carry  on  these  processes 
in  the  squirrel. 

The  bodily  size  of  animals  is  limited,  and  to  this  general 
rule  the  Amceba  is  no  exception,  for  upon  gaining  a  certain 
size,  the  nucleus  divides  into  two  exactly  similar  portions, 
and  very  soon  afterward  the  rest  of  the  body  separates  into 
two  independent  masses  of  equal  size  (Fig.  5,  D),  each  of 
which,  when  entirely  free,  contains  a  nucleus.  In  this  way 
two  daughter  amrabae  are  formed  possessing  exactly  the 
characters  of  the  parent  save  that  they  are  of  smaller  size ; 
but  it  is  usually  not  long  before  they  reach  their  limit  of 
growth,  when  division  occurs  again,  and  so  on,  generation 
after  generation. 

It  not  infrequently  happens,  however,  that  the  pond  or 
stream,  in  which  the  Amoeba  and  other  Protozoa  live,  dries 
up  for  a  portion  of  the  year.  In  such  an  event  the  body 
assumes  a  spherical  shape,  develops  a  firm,  horn-like  mem- 
brane about  itself,  and  thus  encysted  it  withstands  the  sum- 
mer's heat  and  dryness  and  may  be  transported  by  the  wind, 
or  otherwise,  over  great  distances.  When  the  conditions 
again  become  favorable  the  wall  ruptures  and  the  Amoeba 
emerges  to  repeat  its  life  processes. 

15.  Some  relatives  of  the  Amoeba. — All  amoeba-like  forms, 
to  the  number  of  perhaps  a  thousand  species,  possess  this 
same  method  of  locomotion,  but  many  present  some  inter- 


14  ANIMAL   FORMS 

esting  additional  characters.  For  example,  the  form  repre- 
sented in  Fig.  5,  C,  constructs  a  sac-like  skeleton  of  tiny 
pebbles  cemented  together,  into  which  it  may  withdraw  for 
protection.  Others  construct  similar  envelopes  of  lime  or 
flint,  and  still  others,  as  they  continue  to  grow,  build  on 
additional  chambers,  giving  rise  to  a  great  variety  of  forms 
often  of  wonderful  beauty.  In  the  tropics,  particularly, 
some  of  the  shelled  Protozoa  are  so  abundant  that  they  may 
impart  a  whitish  tinge  to  the  water,  and  in  some  places 
their  empty  shells  on  falling  to  the  bottom  form  immense 
deposits.  The  chalk  cliffs  of  England  are  in  large  measure 
made  up  of  such  shells. 

16.  The  Infusoria. — A  little  over  two  hundred  years  ago 
it  was  discovered  that  wherever  water  remained  stagnant  it 
became  favorable  for  the  rapid  multiplication  of  a  large 
number  of  species  of  Protozoa  which  live  in  such  situations. 
These  are  known  as  Infusoria,  and,  like  the  preceding  spe- 
cies, are  usually  of  microscopic  size  and  of  the  most  varied 
shapes.     The  first  striking  feature  of  their  organization  is 
the  presence  of  a  delicate  though  relatively  firm  external 
cell  membrane  known  as  the  cuticle,  which  preserves  a  defi- 
nite shape  to  the  body.     Such  a  method  of  locomotion  as 
exists  in  the  preceding  group  is  consequently  an  impossi- 
bility, but  other  and  more  highly  developed  structures  per- 
form the  office.     These  latter  organs  are  of  two  types,  and 
their  general   characteristics   may  be   readily  understood 
from  an  examination  of  a  few  species  living  in  the  same 
localities  as  the  Ammla. 

17.  The  Euglena. — The  first  type  exists  in  the  common 
fresh-water   organism   known   as   Euglena,  represented  in 
Fig.  6,  A.     Here  the  spindle-shaped  body  is  surrounded  by 
a  delicate  cuticle  perforated  at  one  point,  where  a  funnel- 
shaped  depression,  the  gullet,  leads  into  the   soft  proto- 
plasmic interior.     From  the  base  of  this   depression  the 
protoplasm  is  drawn  out  in  the  form  of  a  delicate  whip-like 
process  known   as  the  flagellum.     This  structure,  always 


THE  PROTOZOA 


permanent  in  form,  constantly  beats  backward  and  forward 
with  great  rapidity  in  a  general  direction  represented  in 
the  diagram  (Fig.  6,  c).  The  movement  from  a  to  b  is 
much  more  rapid  than  the  reverse,  from  b  to  a,  which 
results,  like  the  action  of  the  human  arm  in  swimming,  in 
driving  the  organism  forward.  Not  only  does  the  flagel- 
lum  serve  the  purpose  of  locomotion,  but  it  also  produces 
currents  in  the  water  which 
may  serve  to  bear  minute 
organisms  down  into  the 
gullet,  whence  they  read- 
ily pass  into  the  soft  pro- 


3.  6.  —  Flagellate  Infusoria.  A, 
Euglena  xlridis  ;  c,  pulsating 
vacuole  ;  e,  eye-"spot ;  g,  gullet ; 
w,  nucleus  ;  t,  flagellum.  B,  Co- 
dosiga,  with  collar  surrounding 
the  flagellum.  C,  diagram  illus- 
trating the  action  of  the  flagel- 
lum. All  figures  greatly  enlarged. 


c.v. 


FIG.  7.  —  Paramcecium  aurelia,  a 
ciliate  infusorian.  c,  cilia;  c.v., 
pulsating  vacuotes  ;  /,  food 
particles  ;  g,  gulfet ;  m,  buccal 
groove ;  ».  nucleus. 


toplasm  of  the  body,  there  to  undergo  the  processes  of  di- 
gestion and  assimilation.  In  some  forms  the  protoplasm  in 
the  region  of  the  flagellum  is  drawn  out  in  the  form  of  a 
collar  (Fig.  6,  B),  whose  vibratory  motion  also  aids  in  con- 
veying and  guiding  food  into  the  body. 

18.  The  Slipper  Animalcule. — The  second  type  of  loco- 
motor  organ    may  be   understood  from   a   study  of    the 


16 


ANIMAL  FORMS 


Slipper  Animalcule  (Paramcecium,  Fig.  7),  abundant  in 
stagnant  water.  In  this  form  the  cuticle  surrounding  the 
somewhat  cylindrical  body  is  perforated  by  a  great  number 
of  minute  openings  through  which  the 
internal  protoplasm  projects  in  the  form 
of  delicate  threads.  Each  process, 
termed  a  cilium,  works  on  the  same 
principle  as  the  flagellum,  but  it  beats 
with  an  almost  perfect  rhythm  and  in 
unison  with  its  fellows,  drives  the  an- 
imal hither  and  thither  with  considera- 
ble rapidity. 

On  one  side  of  the  body  is  a  furrow 
which  deepens  as  it  runs  backward  and 
finally  passes  into  the  gullet  (#),  which 
leads  into  the  interior  of  the  body. 
Throughout  the  entire  extent  it  is  lined 
with  cilia  which  create  strong  currents 
in  the  surrounding  water  and  in  this 
way  conduct  food  down  the  gullet  into 
the  body.  Embedded  in  the  outer  sur- 
face of  the  body,  in  among  the  cilia, 
are  also  a  number  of  very  minute  sacks, 
each  containing  a  coiled  thread  which 
may  be  discharged  against  the  body  of 
any  intruder,  so  that  this  form  is  sup- 
plied with  actual  organs  of  defense. 
Two  pulsating  vacuoles  (c.v.)  or  simple 
kidneys  are  also  present,  consisting  of  a 
central  reservoir  into  which  a  number 
of  radiating  canals  extend. 

19.  The  Bell  Animalcule  and  other 
species.— The  Bell  Animalcule  (Vorti- 
cella,  Fig.  8)  is  often  found  in  the  same  situations  as  the 
Slipper  Animalcule,  which  in  certain  respects  it  resembles. 
It  is  generally  attached  by  a  slender  stalk,  and  where  many 


FIG.  S.—Vorticella,  an  at 
tached  ciliate  infusori 
an,  highly  magnified,  a 
fully  extended  Individ 
ual ;  c.v.,  pulsating  va 
cuole  ;  ff,  gullet ;  n,  mi 
cleus.  b,  contractec 
specimen,  c,  small  free 
swimming  individual, 
which  unites  with  a  sta- 
tionary individual  (one 
partly  united  is  shown 
m  specimen  b). 


THE  PROTOZOA  17 

are  growing  together  they  appear  like  a  delicate  growth 
of  mold  upon  the  water  weed.  The  stalk  is  peculiar  in 
being  traversed  by  a  muscle  fiber  arranged  in  a  loose  spiral, 
which  upon  any  unusual  disturbance  contracts  together 
with  the  body  into  the  form  shown  in  Fig.  8,  b. 

These  few  examples  serve  to  show  the  general  plan  of 
organization  and  the  method  of  locomotion  of  the  Infuso- 
ria ;  but,  as  upward  of  a  thousand  species  exist,  with  widely 
differing  habits,  many  interesting  modifications  are  present. 
Some  have  been  driven  in  past  time  to  adopt  a  parasitic 
mode  of  life  within  the  bodies  of  other  animals.  At  pres- 
ent they  are  devoid  of  locomotor  organs,  and  as  they  absorb- 
nutritive  fluids  through  the  surface  of  the  body  all  traces 
of  a  mouth  are  also  absent.  The  reproductive  processes 
also  are  peculiar,  but  they  do  not  concern  us  now. 

20.  Characteristics  common  to  the  Protozoa. — We  have 
now  studied  the  principal  structures  which  serve  in  loco- 
motion among  these  simple  one-celled  forms,  also  the  means 
by  which  they  catch  their  food,  and  we  shall  now  glance  at 
the  internal  processes,  Avhich  are  much  the  same  in  all. 

After  the  food  has  been  taken  into  the  cell,  it  is  prob- 
ably acted  upon  by  some  digestive  fluid,  for  it  soon  assumes 
a  granular  appearance  and  finally  undergoes  complete  solu- 
tion. In  every  case  the  oxygen  is  absorbed  through  the 
general  surface  of  the  body,  and  uniting  with  the  living 
substance,  as  in  the  squirrel,  liberates  the  energy  necessary 
for  the  performance  of  the  animal's  life  work.  The  wastes 
thus  produced  in  a  large  number  of  forms  simply  filter  out 
from  the  body  without  the  agency  of  anything  comparable 
to  a  kidney,  but  in  several  species  they  are  borne  to  a 
definite  spot,  the  pulsating  vacuole  (Figs.  5,  7,  8,  c.v.),  where 
they  gradually  accumulate  into  a  drop  about  the  size  of  the 
nucleus.  The  wall  between  it  and  the  exterior  now  gives 
way  and  the  excretions  are  passed  out.  In  active  indi- 
viduals this  process  may  be  repeated  two  or  three  times  a 
minute,  but  it  is  usually  of  less  frequent  occurrence. 


18  ANIMAL  FORMS 

The  loss  in  bodily  waste  is  continually  made  good  by 
the  manufacture  of  the  food  into  protoplasm,  and  if  the  in- 
come be  greater  than  the  outgo  growth  ensues.  But,  as  in 
all  other  forms,  growth  is  limited,  and  ultimately  the  cell  is 
destined  to  divide,  resulting  in  two  new  individuals.  This 
process  may  be  repeated  many  times,  but  not  indefinitely, 
for  sooner  or  later  various  members  of  the  same  species 
unite  in  pairs  temporarily  or  permanently,  exchange  nu- 
clear material,  and  separate  again  with  apparently  renewed 
energy  and  the  ability  to  divide  for  many  generations. 

21.  Simple  and  complex  animals. — It  is  important  to  note 
that  these  same  processes  of  waste,  repair,  growth,  feeling, 
motion,  and  multiplication  are  the  same  as  those  of  the 
squirrel,  and,  furthermore,  are  common  to  all  living  crea- 
tures, so  that  the  difference  between  animals  is  not  in  their 
activities,  but  in  their  bodily  mechanisms  ;  and  according  to 
the  perfection  of  this,  the  animal  is  high  or  low  in  the 
scale.  Comparing,  for  example,  the  Amoeba  and  Slipper 
Animalcule,  which  are  relatively  low  and  high  Protozoa,  we 
find  in  the  former  that  any  part  of  the  body  serves  in  loco- 
motion and  in  the  capture  of  food,  while  in  the  latter  these 
same  functions  are  performed  by  definite  structures,  the 
cilia  and  gullet.  Now  it  is  well  known  that  a  workman  is 
able  to  make  better  watch-springs,  when  this  is  his  sole 
duty,  than  another  who  must  make  all  parts  of  the  watch ; 
and  likewise  where  a  definite  task  is  performed  by  a  defi- 
nite structure,  it  is  more  efficiently  done  than  where  any 
and  every  part  of  the  body  must  carry  it  on.  So  the 
Amoeba,  in  which  definite  tasks  are  performed  by  any  part 
of  the  body  indifferently,  is  less  perfect  and  thus  lower  than 
the  Paramcecium,  where  these  functions  are  performed  by 
special  organs.  As  we  ascend  the  scale  of  life  we  find  this 
division  of  labor  among  special  parts  of  the  body  more 
complete,  the  organs  and  therefore  the  animal  more  com- 
plex, and  better  fitted  to  carry  on  the  work  of  its  life. 


CHAPTER  IV 


THE   SPONGES 

22.  Their  relation  to  the  Protozoa. — While  the  greater 
number  of  one-celled  forms  are  not  united  with  their  fel- 
lows, there  are  several  species  where  the  reverse  is  true.  In 
Fig.  9,  for  example,  a  fresh-water  form  known  as  Pandorina 
is  represented,  consisting  of  sixteen  cells  embedded  in  a 
spherical,  jelly-like  substance, 
each  one  of  which  is  precisely 
like  its  companions  in  form 
and  activity.  The  aggregation 
may  be  looked  upon  as  a  colo- 
ny of  sixteen  Protozoa  united 
together  to  derive  the  benefit 
of  increased  locomotion  and 
a  larger  amount  of  food  in 
consequence.  As  a  result  of 
such  a  union  they  have  not 
lost  their  independence,  for  if 
one  be  separated  from  the  main 
company  it  continues  to  exist. 

From  such  a  simple  colonial 

type  we  may  pass  through  a  series  of  several  more  complex 
forms  which  reach  their  highest  development  in  the  beau- 
tiful organism,  Volvox  (Fig.  10).  In  this  form  the  indi- 
vidual members,  to  the  number  of  many  thousand,  are  ar- 
ranged in  the  shape  of  a  hollow  sphere.  The  united  efforts 
of  the  greater  number,  which  bear  on  their  outer  surfaces 
two  flagella,  drive  the  colony  with  the  rolling  movement 

19 


FIG.  9.—Pandwina  (from  Nature). 
Highly  magnified. 


20 


ANIMAL  FORMS 


from  place  to  place.  As  just  indicated,  some  individuals 
lack  the  flagella,  and  their  subsequent  careers  show  them 
to  be  of  a  peculiar  type.  Sooner  or  later  each  undergoes 

a  series  of  divisions  form- 
ing a  little  globe  of  cells, 
which  migrates  into  the  in- 
terior of  the  parent  sphere 
and  develops  into  a  new 
colony.  Within  a  short  time 
the  walls  of  the  parent 
break,  liberating  the  im- 
prisoned young,  which  con- 
tinue the  existence  of  the 
species  while  the  parent  or- 
ganism soon  decays. 

Under  certain  circum- 
stances, instead  of  develop- 
*n&  c°l°nies  by  such  a  meth- 

od'  some  of  the  cells  may 

store  up  food  matters  and 
become  eggs,  while  others, 
known  as  sperm-cells,  de- 
velop a  flagellum,  and  sep- 
arating from  the  colony 
swim  actively  in  the  sur- 
rounding water,  where  each 
finally  unites  with  an  egg. 
This  union,  like  that  of  the 
two  individuals  in  Vorticel- 
la  (Fig.  8,  J,  c),  results  in 

tne   POWCr   of   division,  and 


FIG.   10.-A,  Volvox  minor,  entire  colony 

(from  Nature).    B,  C,  and  D,  reproduc-    the  egg  enters  Upon   its    de- 
tive  cells  of  Volvox  globator    All  highly         i  j  .    •  \  • 

magnified.  velopment,   dividing  again 

and  again.    The  cells  so  pro- 

duced remain  together,  form  a  sphere,  and  finally  develop 
a  Volvox  colony. 


THE   SPONGES  21 

In  such  associations  as  Volvox  an  important  step  has 
been  taken  beyond  that  of  Pandorina,  for  there  is  a  division 
of  the  labors  of  the  colony  among  its  various  members, 
some  acting  as  locomotor  cells  while  others  are  germ-cells. 
These  are  now  so  dependent  one  upon  the  other  that  they 
are  unable  to  exist  after  separation  from  the  main  com- 
pany, just  as  a  part  of  the  squirrel  is  incapable  of  leading 
an  independent  existence.  A  higher  type  of  organism  has 
thus  arisen  intermediate  between  the  simple  one-celled 
animals  and  those  of  many  cells,  especially  the  sponges — a 
relation  which  is  more  readily  recognized  after  an  examina- 
tion of  the  latter. 

23.  Development  of  the  sponge. — As  with  all  many- 
celled  animals,  the  sponge  begins  its  existence  as  an  egg, 
in  this  case  barely  visible  to  the  sharp  unaided  eye.  Fer- 
tilized by  its  union  with  a  sperm  cell,  development  com- 
mences, and  the  first  apparent  indication  of  the  process 
will  be  the  division  of  the  cell  into  two  halves  (Fig.  11,  A,  B). 
Each  half  redivides  into  four,  these  again  into  eight  cells, 
and  this  process  is  repeated,  giving  the  young  sponge  the 
general  form  of  Pandorina.  The  divisions  of  the  cells 
still  continue  and  result  in  the  formation  of  a  hollow 
globe  of  cells  (called  the  Uastula,  Fig.  11,  E,  F)  similar 
to  Volvox,  and  at  this  point  the  young  larva  leaves  the 
parent. 

The  next  transformation  consists  in  a  pushing  in  of  one 
side  of  the  sphere,  just  as  one  might  press  in  the  side  of  a 
hollow  rubber  ball.  The  depression  gradually  deepens,  and 
finally  results  in  the  formation  of  a  two-layered  sac  known 
as  the  gastrula  (Fig.  11,  G).  At  this  stage  of  its  existence 
the  sponge  settles  down  for  life  in  some  suitable  spot,  by 
applying  the  opening  of  its  sac-like  body  to  some  foreign 
object.  In  assuming  the  final  form  a  new  mouth  breaks 
through  what  was  once  the  bottom  of  the  sac,  canals  per- 
forate the  body  wall,  a  skeleton  is  developed,  and  the  char- 
acteristic features  of  the  adult  are  thus  attained. 


ANIMAL   FORMS 


24.  Distribution. — The  sponges  are  aquatic  animals,  and, 
with  the  exception  of  one  family  consisting  of  relatively 
few  species,  all  are  inhabitants  of  the  sea  in  every  part  of 


FIG.  11. — Diagrams  illustrating  the  development  of  a  sponge.  A,  egg-cell ;  n,  nu- 
cleus. B,  C,  D,  2-,  4-,  and  16-cell  stages.  E,  blastula.  F,  section  through  some- 
what older  larvre.  G,  gastrula.  H,  young  sponge.  I,  section  through  somewhat 
younger  larvse  than  H. 

the  globe.  The  larger  number  occupy  positions  along  the 
shore,  becoming  especially  abundant  in  the  tropics ;  but 
other  species  occur  at  greater  depths,  several  species  living 


THE  SPONGES  23 

between  three  and  four  miles  from  the  surface.  Unlike 
the  majority  of  animals,  all  members  of  this  group  are 
securely  fastened  to  some  foreign  object,  such  as  rocks,  the 
supports  of  wharves,  or  with  one  extremity  embedded  in 
the  sand.  As  we  have  seen,  the  young  enjoy  a  free-swim- 
ming existence  and  are  swept  far  and  wide  by  means  of 
tidal  currents,  but  sooner  or  later  these  migrations  are 
terminated  ?n  some  suitable  locality,  where  the  sponge 
passes  the  remainder  of  its  existence.  During  this  time 
some  species  may  never  exceed  the  size  of  a  mustard-seed, 
while  others  attain  a  diameter  of  three  feet,  or  even  more. 
Sponges  also  vary  exceedingly  in  shape,  some  having  the 
form  of  thin  encrusting  sheets,  others  being  globular,  tubu- 
lar, cuplike,  or  highly  branched  (Fig.  12). 

25.  The  influence  of  their  surroundings. — In  by  far  the 
larger  number  of  cases  an  animal  possesses  the  bodily  form 
of  the  parent.  External  agencies  may  modify  this  to  some 
extent,  but  usually  only  to  a  limited  degree.  A  squirrel, 
for  example,  resembling  its  parent,  may  grow  to  a  relatively 
large  or  stunted  size  according  to  the  food  supply,  and  it 
may  become  strong  or  weak  according  to  the  amount  of 
exercise,  and  various  other  changes  may  result  owing  to 
outside  causes ;  but  as  a  result  of  these  influences  the 
animal  is  rarely  so  modified  that  one  is  unable  to  distinguish 
the  species.  Many  of  the  sponges,  however,  are  exceptions 
to  this  general  rule.  If,  for  example,  some  of  the  young 
of  a  certain  parent  develop  in  quiet  water  or  in  an  un- 
favorable locality,  they  will  usually  be  low,  flat,  and  un- 
branched ;  while  the  others,  growing  in  swiftly  running 
waterways,  develop  into  tall,  comparatively  delicate  and 
highly  branched  individuals.  Under  such  circumstances 
not  only  does  the  external  form  become  modified,  but 
the  internal  organization  may  undergo  profound  change. 
The  entire  organism  is  plastic  and  readily  molded  by 
the  influence  of  its  surroundings,  and  the  consequent 
lack  of  definite  characters  often  renders  it  impossible 


ANIMAL  FORMS 


to   assign   such   forms   to  a  definite   position   among   the 

sponges. 

26.  Structure  of  a  simple  sponge. — In  the  simpler  sponges 

the  body  is  usually  vase-shaped  (Fig.  13),  with  the  base 

fastened  to  some  foreign 
object,  while  at  an  oppo- 
site end  an  opening  leads 
into  a  comparatively  large 
internal  cavity.  This  lat- 
ter space  is  also  put  in 
communication  with  the 
exterior  by  a  multitude  of 
minute  pores  which  pene- 
trate the  body  wall.  In 


FIG.  12. — Various  forms  of  sponges,  natural  size.    (From  Nature.) 

the  living  condition  currents  of  water  continually  pass 
through  these  smaller  canals,  and  out  of  the  large  termi- 
nal opening,  thus  bringing  within  reach  of  the  body  minute 


THE  SPONGES 


floating  organisms  or  organic  remains  which  serve  as  food. 
The  mechanism  by  which  this  process  is  effected,  and  the 
various  other  structures  of  the  body,  are  in  large  part  invis- 
ible from  the  exterior,  requiring  the 
study  of  thin  sections  of  the  sponge 
to  make  them  clearly  understood. 

Under  the  microscope  such  a  sec- 
tion shows  the  body  of  a  sponge  to 
consist  of  an  immense  number  of  va- 
riously formed  cells  constituting  three 
distinct  layers  (Fig.  14).  Xot  only 
do  these  layers  consist  of  different 
kinds  of  cells,  but  the  duties  per- 
formed by  each  are  different.  For  ex- 
ample, a  glance  at  Fig.  14  will  show 
that  in  the  inner  layer  certain  colum- 
nar cells  exist,  provided  with  a  fla- 
gellum  and  encircling  collar,  the  ap- 
pearance being  strikingly  like  certain 
of  the  Protozoa  (Fig.  6,  B).  During 
life  their  whip-like  processes,  lashing 
backward  and  forward  in  perfect  uni- 
son, produce  currents  of  water  which 
continually  pass  through  the  body. 
The  food  thus  entering  the  animal  is 
taken  up  by  the  cells  of  the  inner 
layer  as  it  passes  by.  The  supply, 
however,  is  usually  more  than  suffi- 
cient to  meet  the  demands  of  this 
layer,  and  the  excess  is  passed  on  to 
the  middle  and  outer  layers.  The 
exact  method  by  which  this  occurs  is  still  a  matter  of 
doubt,  but  there  seems  to  be  little  question  but  that 
each  cell  of  the  body  receives  its  food  in  a  practically  un- 
modified condition,  requiring  that  it  digest  as  well  as 
assimilate.  The  oxygen  necessary  to  this  latter  process 


FIG.  13.— One  of  the  sim- 
plest sponges  (Calcolyn- 
tlnm  primigenius  (after 
HAECKEL).  A  portion 
of  the  wall  has  been  re- 
moved to  show  the  in- 
side. 


ANIMAL   FORMS 


is  absorbed  by  all  parts  of  the  body  in  contact  with  the 

water. 

27.  Skeleton  of  sponges. — When  it  is  remembered  that 

the  protoplasm  composing  the  cells  of  the  sponge  has  about 

the  same  consistence 
as  the  white  of  egg, 
it  will  be  readily  un- 
derstood why  the 
greater  number  of 
sponges  possess  a  skel- 
eton. Without  such 

FIG.  14.-Portion  of  wall  of  sponge,  showing  three  &    support    the    larger 
layers,    e,  outer  layer  ;  i,  inner  layer,  consisting  rr  ° 

of  collared  cells  ;  TO,  middle  layer,  consisting  of  globular   Or  branched 

irregular  cells,  among  which  are  the  radiate  epic-  formg    could    not    CX- 
ules  and  egg-celte.  .         , 

ist,  and  even  in  the 

smaller  members  there  would  be  danger  of  a  collapse  of  the 
body  walls  and  consequent  stoppage  of  the  food  supply, 
owing  to  the  closure  of  the  pores.  So  in  all  but  a  very  few 
thin  or  flat  forms  a  skeleton  appears  in  the  young  sponge 
almost  before  growth  ..... 
has  fairly  begun,  and 
this  increases  with  the 
body  in  size  and  com- 
plexity. It  is  formed 
by  the  activity  of  the 
cells  of  the  middle  layer, 
and  may  be  composed 
either  of  a  lime  com- 
pound resembling  mar- 
ble, or  of  flint,  or  of  a 
horn-like  substance  resembling  silk,  or  these  may  exist  in 
combination  in  certain  species.  When  consisting  of  either 
of  the  first-named  substances  it  is  never  formed  in  one 
continuous  piece,  but  of  a  vast  multitude  of  variously  shaped 
crystal-like  bodies  termed  spicules  (Fig.  15).  These  occur 
everywhere  throughout  the  body,  firmly  bound  together 


\ 


FIG.  15. — Different  types  of  sponge  spicules. 


THE  SPONGES  27 

by  means  of  cells,  or  so  interlocked  that  they  form  a  rigid 
support  to  which  the  fleshy  substance  is  bound  and  through 
which  the  numerous  canals  penetrate. 

In  a  relatively  few  species  only  does  the  skeleton  con- 
sist of  horn,  though  there  are  many  in  which  horn  and  flint 
exist  together.  In  the  former  event,  if  the  skeleton  be 
elastic  and  of  sufficient  size,  it  becomes  valuable  to  others 
than  the  naturalist,  for  the  familiar  sponges  of  commerce 
are  the  horny  skeletons  of  forms  usually  taken  in  the  West 
Indies  or  in  the  Mediterranean  Sea.  In  these  localities  the 
animals  are  pulled  off  by  divers,  or  with  hooks,  and  are  then 
spread  out  in  shallow  water  where  the  protoplasmic  sub- 
stance rapidly  decays.  The  remaining  skeleton,  thoroughly 
washed  and  dried,  is  ready  for  the  markets  of  the  civilized 
world. 

Examining  a  bit  of  such  a  "  sponge  "  under  a  magnify- 
ing glass,  it  will  be  seen  that  the  skeleton  is  not  composed 
of  various  pieces,  but  of  one  continuous  mass  of  branching 
fibers,  which  interlace  and  unite  in  apparently  the  greatest 
confusion ;  yet  in  the  living  animal  these  were  perfectly 
adapted  to  the  position  of  the  canals  and  the  general  needs 
of  the  animal. 

Besides  being  a  scaffold-work  to  which  the  fleshy  portions 
of  the  body  are  fastened,  the  skeleton  serves  also  for  pro- 
tection. In  some  species,  needle-like  spicules  as  fast  as 
they  are  formed  are  partly  pushed  out  over  the  entire  sur- 
face of  the  body,  giving  the  appearance  of  a  spiny  cactus ; 
or  in  other  cases  they  are  arranged  in  tufts  about  the  canals, 
effectually  preventing  the  entrance  of  any  marauder. 
Thus  perfectly  protected,  the  sponges  have  but  few  natural 
enemies,  and  hence  it  is  that  in  favorable  localities  they 
grow  in  great  profusion. 

28.  Race  histories  and  life  histories. — We  have  now  traced 
living  things  from  their  simplest  beginnings,  where  they 
exist  as  single  cells,  and  have  seen  that  in  bygone  times 
similar  forms  have  united  into  simple  colonies,  and  these 


28  ANIMAL  FORMS 

through  a  division  of  labor  among  the  constituent  cells 
have  resulted  in  Volvox-\ike  colonies.  There  are  the  strong- 
est reasons  for  the  belief  that  as  these  simple  forms  scat- 
tered into  various  surroundings  and  underwent  changes  to 
meet  the  shifting  conditions,  they  assumed  different  de- 
grees of  complexity  that  have  resulted  in  the  animal  forms 
of  the  present  day. 

It  may  have  been  noticed  also  that  the  sponge  in  its 
development  passes  through  these  stages  :  a  single-celled 
egg ;  later,  a  young  form  similar  to  Pandorina,  then  growing 
to  look  like  Volvox,  and  finally  assuming  its  permanent  form. 
The  history  of  the  race  of  sponges  and  their  development 
through  a  long  line  of  ancestry  of  increasing  complexity  is 
thus  told  by  the  sponge  as  it  develops  from  the  egg  into 
the  adult ;  and,  so  far  as  we  know,  all  the  many-celled  ani- 
mals in  their  growth  from  the  egg  repeat  more  or  less 
clearly  the  stages  passed  through  by  their  forefathers. 


CHAPTEE  V 

THE    CCELENTEBATES 

29.  General  remarks. — This  division  of  the  roany-eelled 
animals  includes  the  jelly-fishes,  sea-anemones,  and  corals. 
A  few  species  live  in  fresh  water,  but  the  majority  are  con- 
fined to  the  sea,  being  found  everywhere  from  the  shore- 
line  and   ocean   surface  to  the    most    profound    depths. 
Adapted  to  different  surroundings  and  modes  of  life,  they 
constitute  a  vast  assemblage  of  the  most  bewildering  di- 
versity.    In  some  cases  their  resemblance  to  plants  is  re- 
markable, and  the  term  zoophyte  or  "  plant  animal,"  occa- 
sionally applied  to  them,  is  the  relic  of  former  times  when 
naturalists  confounded  them  with  plants.     Even   to-day 
certain  species  are  sometimes  collected  and  preserved  as 
seaweeds  by  the  uninformed. 

The  general  plan  on  which  all  co3lenterates  are  con- 
structed is  a  simple  sac,  in  some  respects  resembling  that 
of  the  lower  sponges,  yet,  since  the  modes  of  life  of  the 
members  of  the  two  groups  are  usually  quite  unlike,  we 
shall  find  many  profound  differences  between  them. 

30.  The  fresh-water  Hydra.— The  bodily  plan  comes  out 
most  clearly  in  the  Hydra  (Fig.  16,  A,  D),  which  occurs 
upon  the  stems  and  leaves  of  submerged  fresh-water  plants 
in  this  and  other  countries.    Its  body,  of  a  green  or  grayish 
color,  according  to  the  species,  scarcely  ever  attains  a  diam- 
eter greater  than  that  of  an  ordinary  pin  nor  a  length  ex- 
ceeding half  an  inch.     One  end  of  the  cylindrical  organism 
is  attached  to  some  foreign  object  by  means  of  a  sticky 
secretion,  but  as  occasion  requires  it  may  free  itself,  and  by 

29 


30 


ANIMAL   FORMS 


means  of  a  "  measuring-worm  "  movement  travel  to  another 

place. 

Examined  under  a  hand  lens,  the  free  end  of  the  body 

will  be  found  to  support  six  to  eight  prolongations  known 

as  tentacles,  which 
serve  to  convey 
food  to  the  mouth, 
centrally  located 
in  their  midst. 
This  opening,  un- 
like that  of  the 
sponges,  is  the 
only  one  leading 
directly  into  the 
large  central  gas- 
tric cavity  which 
occupies  nearly 
the  entire  animal 
(Fig.  16,  D).  As 
in  the  sponge,  the 
cells  of  the  body 


v  the  form  of  defi- 
nite layers,  but  the 
middle  one  is  rep- 
resented only  by 
a  thin  gelatinous 
sheet. 

31.    Organs    of 
defense.  —  These 

FIG.  16. — The  fresh-water  Hydra.    A.  entire  animal,  de- 

veloping  a  new  individual  (enlarged  25  times).     B;  C,    are    the     SO-Called 
nettle-cells  (after  SCHNEIDER)  ;    D,  section  through    lasso  or  nettle-cells 

(Fig.  16,  C).  Some 

of  the  cells  of  the  outer  layer  possess,  in  addition  to  the 
elements  of  the  typical  cell,  a  relatively  large  spherical  sac 
filled  with  a  fluid,  and  also  a  spirally  wound  hollow  thread 


THE  CCELENTE  RATES  31 

provided  with  barbs  near  its  base.  On  the  outer  extremity 
of  the  nettle-cell  projects  a  delicate  bristle-like  process,  the 
trigger  hair.  These  cells  are  especially  abundant  on  the 
tentacles  (Fig.  16,  A,  D),  forming  close,  knob-like  eleva- 
tions or  "  batteries,"  thus  rendering  it  practically  impossi- 
ble for  any  free-swimming  organism  to  avoid  touching  them 
in  brushing  against  the  body.  In  such  an  event  the  dis- 
turbances conveyed  through  the  trigger  hair  set  up  in  some 
unknown  way  very  rapid  changes  in  the  cell.  This  causes 
the  sac  to  discharge  the  coiled  thread  and  barbs  into  the 
body  of  the  intruder,  which  is  rendered  helpless  by  the  par- 
alyzing action  of  the  fluid  conveyed  through  the  thread. 
Thus  benumbed  it  is  rapidly  borne  to  the  mouth  and  swal- 
lowed. In  time  new  nettle-cells  develop  to  take  the  place 
of  those  discharged  and  consequently  worthless. 

32.  Digestion  of  food.— Upon  the  interior  of  the  body  of 
Hydra  and  all  of  the  coalenterates  the  food,  by  reason  of  its 
large  size,  is  incapable  of  being  taken  into  the  various  cells. 
It  is  necessary,  therefore,  to  break  it  up  into  smaller  masses, 
and  this  is  accomplished  through  the  solvent  action  of  the 
digestive  fluid  poured  over  it  from  some  of  the  cells  of  the 
adjacent  inner  layer.     When  subdivided,  the  granules  swept 
about  the  gastric  cavity  by  the  beating  of  the  flagella  (Fig. 
16,  D)  are  seized  by  the  processes  on  the  free  surfaces  of  the 
remaining  inner  layer  cells,  where  they  undergo  the  final 
stages  of  digestion  ;  then  in  a  dissolved  state  they  become 
absorbed  and  assimilated  by  all  the  cells  of  the  body. 

33.  Methods  of  multiplication. — Very  frequently,  espe- 
cially if  the  Hydra  has  been  well  fed,  two  or  three  pro- 
cesses arising  as   outpushings   of  the  body  wall   may  be 
noted  upon  the  sides  of  the  animal  (Fig.  16,  A,  D).     If 
these  be  watched  from  time  to  time  they  are  found  to  in- 
crease in  size,  and  finally,  upon  their  free  extremities,  to 
develop  a  mouth  and  surrounding  tentacles.     Up  to  this 
point  growth  has  taken  place  as  a  result  of  the  assimilation 
of  nutritive  substances  supplied  from  the  parent ;  but  a  con- 


32 


ANIMAL  FORMS 


striction  soon  occurs  which 
separates  the  young  from  the 
parent,  and  from  that  time 
on  the  two  lead  independent 
existences.  At  other  times 
this  asexual  method  of  mul- 
tiplication is  replaced  by  sex- 
ual reproduction,  where  new 
individuals  arise  from  fertil- 
ized eggs.  Both  eggs  and 
sperm  arise  in  Hydra  and  in 
some  other  animals  in  the 
same  individual,  but  in  all 
such  cases  the  eggs  are  fertil- 
ized by  sperm  which  escape 
from  some  other  individual. 
The  fertilized  egg,  surround- 
ed by  a  firm  coat,  separates 
from  the  parent,  drops  to  the 
bottom,  and  after  a  period  of 
rest  develops  into  a  little  Hy- 
dra which  hatches  and  enters 
upon  a  free  existence. 

FIG.  17.— Different  types  of  Hydrozoan 
colonies.  From  Nature,  the  lower 
species  magnified  about  50  diameters. 


THE   CtELENTERATES  33 

34.  Hydrozoa,  or  Hydra-like  animals.— Attention  has  al- 
ready been  directed  to  the  fact  that  the  structure  of  Hydra 
is  the  simplest  of  the  coelenterates  ;  nevertheless,  the  thou- 
sand or  more  species  belonging  to  this  class  which  present 
a  much  more  complicated   appearance  (Fig.    17)   possess 
many  fundamental  Hydra-like  characters.     It  is  owing  to 
this  fact  that  this  assemblage  of  forms  has  been  placed  in 
the  class  of  the  Hydrozoa,  or  Hydra-like  animals. 

With  but  very  few  exceptions  the  members  of  this  class 
are  marine,  usually  living  near  the  shore-line,  where  at 
times  their  plant-like  bodies  occur  in  the  greatest  profusion 
attached  to  rocks,  seaweeds,  or  the  bodies  of  other  animals, 
particularly  snails  and  crabs.  Fig.  17  (upper  colony)  gives 
a  good  idea  of  one  of  the  more  complex  forms,  whose  tree- 
like body  attains  in  some  cases  the  relatively  giant  height  of 
from  15  to  25  c.m.  (six  to  ten  inches).  In  early  life  it  bears 
a  close  resemblance  to  a  Hydra.  Buds  form  in  much  the 
same  way,  but  they  retain  permanently  their  connection  with 
the  parent,  and  in  turn  bear  other  buds,  until  finally  the  form 
shown  in  the  figure  is  attained.  In  the  meantime  root-like 
processes  have  been  forming  which  afford  firm  attachment 
to  the  object  upon  which  the  body  rests.  Also  during  this 
process  the  cells  of  the  outer  layer  form  a  horny  external 
skeleton  ensheathing  the  entire  organism  except  the  ter- 
minal portions  (the  hydranths,  Fig.  18,  B)  bearing  the  ten- 
tacles. The  gastric  cavities  of  all  communicate,  and  the 
food  captured  by  one  ministers  in  part  to  its  own  needs 
and,  swept  through  the  tubular  stalks  and  roots,  is  also 
shared  by  all  other  members. 

35.  Jelly-fishes  and  the  part  they  play.— During  the  pro- 
cess of  growth  a  number  of  stubby  branches  arise  which 
differ  from  the  ordinary  type  in  shape,  and  also  in  many 
cases  as  regards  color/  .  These  club-like,  fleshy  portions  de- 
velop close-set  buds  (Fig.  18,  c)  which  early  assume  a  bell- 
like  shape,  the  point  of  attachment  corresponding  to  the 
handle,  while  the  clapper  is  represented  by  a  short,  slender 


34  ANIMAL  FORMS 

process  bearing  on  its  end  an  opening  which  becomes  the 
mouth  (Fig.  18,  A).  Around  the  margin  of  the  bell  nu- 
merous tentacles  develop,  and  at  the  same  time  the  gelati- 
nous substance  situated  between  the  outer  and  inner  layers 
of  the  bell  expands  to  a  relatively  enormous  degree,  giving 
it  an  increasing  globular  form  and  glassy  appearance. 


FIG.  18.— A  jelly-fish  (Gonionemus),  slightly  enlarged.  The  stalked  mouth  is  shown 
in  dotted  outline.  B.  C,  enlarged  portions  of  a  hydroid  colony  bearing  the 
mouth  and  tentacles  ;  j,  a  capsule  within  which  the  jelly-fish  develop  ;  D,  dia- 
gram of  jelly-fish,  illustrating  its  method  of  locomotion. 

Finally,  vigorous  movements  rupture  the  connection  with 
the  parent,  and  this  newly  developed  outgrowth,  usually 
small,  becomes  an  independent  organism  popularly  termed 
a  jelly-fish.  While  the  external  form  of  the  jelly-fish  appears 
to  be  widely  different  from  the  hydranths,  a  more  careful 
study  shows  the  difference  to  be  superficial.  Some  zoolo- 
gists believe  that  jelly-fishes  are  simply  buds  which  have 
become  fitted  to  separate  and  swim  away  from  the  colony 
in  order  to  distribute  the  young,  as  described  hereafter. 
When  the  stalked  colonies  are  very  abundant  the  jelly- 


THE  CCELENTERATES  35 

fishes  may  be  liberated  in  such  multitudes  that  the  upper 
surface  of  the-  ocean  for  many  miles  may  be  closely  packed 
with  them  in  numbers  reaching  far  into  the  millions.  In 
these  positions  they  are  carried  both  by  oceanic  currents 
and  through  the  alternate  expansion  and  contraction  of  the 
bell,  a  movement  resembling  the  partial  closing  and  open- 
ing of  an  umbrella.  In  the  jelly-fish  the  contraction  is  the 
more  vigorous  and  rapid,  and  as  it  takes  place  the  opening 
in  the  velum  or  veil  (Fig.  18, 5)  is  so  narrowed  that  the  water 
in  the  subumbrella  space  (a)  is  driven  through  it  with  con- 
siderable force,  which  results  in  driving  the  body  in  the 
opposite  direction. 

The  life  of  a  jelly-fish  is  perhaps  of  short  duration,  last- 
ing not  more  than  a  few  hours  in  some  species,  up  to  two 
or  three  weeks  in  others,  but  during  that  period  they  pro- 
duce multitudes  of  eggs  which  develop  into  minute  free- 
swimming  young.  These  settle  down  on  some  rock  or  sea- 
weed, and  soon  develop  a  Hydra-like  body  which,  after  the 
fashion  described  above,  grows  into  another  tree-like  colony. 

36.  Alternation  of  generations. — It  will  be  noticed  that 
the  offspring  of  the  jelly-fishes  are  not  jelly-fishes,  but  stalked 
colonies,  and  these  latter  forms  give   rise  to  jelly-fishes. 
This  is  known  as  the  alternation  of  generations,  the  jelly- 
fish generation  alternating  with  the  colonial  form.     This 
characteristic  is  of  the  greatest  service  in  preventing  the 
extermination   of   the  race.     Were   the  stalked  forms  to 
give  rise  directly  to  other  stationary  colonies,  it  is  obvious 
that  before  long  all  the  available  space  in  the  immediate 
locality  would  be  filled.     The   food   supply,  always  lim- 
ited, would  not  suffice,  and  starvation  of  some  or  imper- 
fect development  of  all  would  result ;  but  by  means  of  the 
free-swimming  jelly-fish  new  colonies  are  established  over 
very  extensive  areas,   and  favorable  situations  are   held 
by  all. 

37.  More  complex  types. — As  mentioned  above,  there  are 
perhaps  upward  of  a  thousand  species  of  Hydrozoa,  all  with 


36 


ANIMAL   FORMS 


essentially  the  same  structure  but  with  various  modes  of 
branching  (for  some  of  the  commoner  modes,  see  Fig.  17)- 
In  some  of  the  higher  forms  a  division  of  labor  has  arisen 
among  various  members  of  the  association  which  has  led  to 
most  interesting  results.  For  example,  Fig.  19  represents 
a  species  of  hydroid  found  investing  the  shells  of  sea-snails 
occupied  by  hermit  crabs  (Fig.  60).  To  the  unaided  eye 
its  appearance  is  that  of  a  delicate  vegetable  growth,  but 
when  placed  under  the  microscope  it  is  found  to  consist  of 

a  multitude  of  Hydra-like 
animals  united  by  a  hollow 
branching  root  system  con- 
necting the  gastric  cavities 
of  all  of  them  (Fig.  19). 
Certain  individuals  (a) 
with  tentacles  and  a  mouth 
resemble  a  Hydra ;  others, 
without  a  mouth  and  ten- 
tacles, are  reduced  to  a 

FIG.  19.-An  enlarged  portion  of  a  hydroid    club-like    form    (b)  liberally 


colony  (Ilydracliniq),  showing  (a)  the 
nutritive  polyp,  (b)  the  defensive  polyp, 
and  (c)  the  reproductive  polyp. 


supplied  with  nettle-cells 
upon  their  free  extremi- 
ties; while  the  third  type 
(c),  likewise  devoid  of  a  mouth,  possesses  rudiments  of  ten- 
tacles below  which  are  borne  numerous  clumps  of  repro- 
ductive cells.  The  first  type,  the  only  one  possessing  a 
mouth,  captures  the  food,  and  after  digesting  it  distributes 
the  greater  portion  to  the  remaining  members  by  means  of 
the  connecting  root  system ;  those  of  the  second  form,  de- 
fending the  others  by  means  of  their  nettle-cells  against 
the  inroads  of  a  foreign  enemy,  are  the  soldiers  of  the  colo- 
ny; while  the  third  type  produces  the  eggs  from  which 
new  individuals  develop. 

In  some  of  the  higher  Hydrozoa,  the  Portuguese  man- 
of-war  (Fig.  20),  this  division  of  labor  has  reached  a  more 
advanced  stage  of  development,  and  in  addition  the  entire 


THE   CCELENTERATES 


37 


colony  is  fitted  for  a  free-swimming  existence.  "What  cor- 
responds ordinarily  to  the  attached  stalk  in  other  forms 
terminates  in  a  bladder-like  expansion,  distended  with 
gas,  that  serves  as  a  float.  From  it  are  suspended  individ- 
uals resembling  great  stream- 
ers sometimes  many  feet  in 
length,  without  mouths,  but 
loaded  with  nettle-cells  that 
enable  them  to  capture  the 
food,  which  is  conveyed  to  the 
second  type,  the  nutritive 
polyps.  Each  of  these  is  a 
simple  tube  bearing  a  mouth, 
and  within  them  the  food  is 
digested  and  distributed  by 
means  of  a  branching  gastric 
cavity  extending  throughout 
the  entire  colony.  Then  there 
are  individuals  like  mouthless 
jelly-fishes  which  bear  'the 
eggs  and  care  for  the  perpet- 
uation of  the  colony ;  and  be- 
sides these  there  may  be  some 
whose  duty  it  is  to  defend  the 
rest,  and  others  whose  active 
swimming  movements,  to- 
gether with  the  wind,  drive 
the  colony  about.  Thus  uni- 
ted, sharing  the  food  supply 
and  working  for  the  general  welfare  of  all,  the  members  of 
this  colony  live  in  greater  security  and  with  less  effort  than 
if,  as  separate  individuals,  each  was  fighting  the  battles  of 
life  alone. 

38.  Scyphozoa.— The  greater  number  of  the  larger  and 
more  conspicuous  jelly-fishes  are  included  under  this  term. 
In  general  shape  and  locomotion  they  resemble  those  of  the 


PIG.  30. -A  colonial  jelly-fish  (Physaiia). 
From  Nature. 


ANIMAL  FORMS 


preceding  group  (Fig.  21),  but,  while  the  latter  are  generally 
very  small,  these  forms  are  commonly  from  four  to  twelve 
inches  in  diameter,  and  some  measure  one  to  two  meters 
(three  to  six  feet)  across  the  bell.  They  are  also  distin- 
guished by  means  of  tentacles  which  extend  from  the  cor- 
ners of  the  mouth  sometimes  to  a  distance  of  several  feet, 

and  together  with  the 
marginal  tentacles  are 
formidable  weapons  for 
capturing  small  crabs, 
fishes,  and  other  ani- 
mals which  serve  as 
food.  In  turn  these 
forms  serve  as  the  food 
of  many  whales,  por- 
poises, and  numerous 
fishes  which  hunt  them 
down,  though  the 
amount  of  nourishment 
they  contain  is  prob- 
ably relatively  small 
owing  to  the  fact  that 
in  their  composition 
there  is  a  large  percent- 
age of  water  (99  per 
cent  in  some  species).  The  lobed  margin  of  the  bell,  the 
absence  of  a  definite  swimming  organ  or  velum,  and  the 
character  of  several  of  the  internal  organs,  distinguish  the 
larger  from  the  smaller  jelly-fish  ;  but  the  greatest  differ- 
ence, however,  is  in  the  method  of  development. 

39.  Development. — The  eggs  arise  from  the  inner  layer 
of  the  jelly-fish  and  drop  into  the  gastric  cavity,  where  each 
develops  into  a  ciliated  two-layered  sac  in  some  respects 
like  that  of  a  young  sponge.  Swimming  away  from  the 
parent,  they  finally  settle  down,  and  attaching  themselves 
(Fig.  22,  a)  assume  the  external  form  and  habits  of  the  sea- 


?IG.  21.— A  jelly-flsh  (Rkizostmna),  about  one- 
fourth  natural  size. 


THE   CCELENTERATES 


39 


anemones,  described  in  the  next  section.     In  the  course  of 
time  remarkable  changes  ensue,  which  first  manifest  them- 


FIG.  22.— Stages  in  the  development  of  a  scyphozoan  jelly-fish,  a,  the  attached 
young,  which  in  b  has  separated  into  a  number  of  disks,  each  of  which  becomes  a 
jelly-fish,  c.—  After  KOBSCHBLT  and  HEIDEB. 

selves  in  a  series  of  grooves  encircling  the  body.  These 
grow  deeper,  and  the  body  of  the  animal  finally  comes  to 
resemble  a  pile  of  sau- 
cers with  the  edge  of 
each  developed  into  a 
number  of  lobes  (Fig. 
22,  #).  One  after  an- 
other each  saucer,  to 
preserve  the  simile, 
raises  itself  from  the 
top  of  the  pile  and 
swims  away,  and  is 
clearly  seen  to  be  a 
jelly-fish,  though  con- 
siderably unlike  the 

adult.      As  growth  pro-  FlG-  23-An  att*ched  ^yphozoan  Jelly-fish 

1  (Halidystus).    Natural  size,  from  Nature. 

ceeds,  however,  it  un- 
dergoes a  series  of   transformations  which  result  in  the 
adult  form. 

4 


40  ANIMAL   FORMS 

40.  Sea-anemones. — In  its  external  appearance  the  sea- 
anemone  (Fig.  24)  bears  some  resemblance  to  the  Hydra,  but 
is  of  a  much  larger  size  (1  to  45  c.m.,  or  |  inch  to  1£  feet 
in  diameter),  and  is  frequently  brilliantly  colored.  The 
number  of  tentacles  is  also  more  numerous,  and  the  mouth 
leads  into  the  body  by  means  of  a  slender  esophagus  (Fig. 
25).  Numerous  partitions  from  the  body  wall  extend  in- 
ward, and  many  unite  to  the  esophagus,  keeping  the  latter 


FIG.  24. — Sea  anemones  (.the  two  upper 


;ary  coral  polyps. 


in  position.  Below  the  esophagus  each  partition  projects 
into  the  great  cavity  of  the  body  and  bears  upon  its  inner 
free  edge  several  important  structures.  The  first  of  these, 
known  as  the  mesenteric  filaments  (Fig.  25),  appearing  like 
delicate  frills,  plays  an  active  part  in  the  digestion  of  the 
food.  Associated  with  these  are  long,  slender  threads, 


THE  CCELENTERATES 


closely  packed  with  innumerable  lasso-cells,  which  may  be 
thrown  out  through  openings  in  the  body  wall  when  the 
animal  is  attacked.  Lasso-cells  are  also  very  numerous  on 
the  tentacles,  which  are  thus  to  some  extent  defensive,  but 
are  chiefly  active  in  capturing  the  crabs  and  small  fish 
which  serve  as  food. 

The  partitions  also  carry  eggs  which  may  undergo  the 
first  stages  of  their  growth  within  the  body,  and  when 
finally  able  to  swim 
are  sent  out  through 
the  mouth  opening 
by  hundreds  to  seek 
out  favorable  situa- 
tions, there  to  set- 
tle down  and  re- 
main. In  some  spe- 
cies the  young  may 
sometimes  arise  as 
buds,  as  in  Hydra 
(Fig.  24),  and  in 
others  the  animals 
have  been  described 
as  splitting  longi- 
tudinally into  two 
equal-sized  young. 

41.  Corals.— The 
coral    polyps    also 

belong  to  this  group,  showing  a  very  close  resemblance  to 
the  sea-anemones.  In  most  cases  they  develop  a  firm  skel- 
eton of  lime,  commonly  known  as  "  coral,"  which  serves  to 
protect  and  support  the  body.  In  a  few  species  the  polyps 
throughout  life  are  solitary,  and  with  skeleton  comparative- 
ly simple  (Fig.  24) ;  but  the  larger  number  of  species  be- 
come more  complex  by  developing  buds,  which  retain  their 
connection  with  the  parent,  and  in  turn  produce  other  out- 
growths with  the  ultimate  result  that  highly  branched 


FIG.  25.— Longitudinal  section  through  the  body  of  a 
sea-anemone,  oe,  esophagus;  m.  /.,  mesenterial 
filaments  ;  r.,  reproductive  organs. 


42  ANIMAL  FORMS 

colonies  are  produced  (Fig.  26).  At  the  same  time  the 
outer  layer  of  the  body  is  continually  forming  a  skeleton 
which  encloses  the  colony  as  a  sheath,  except  at  the  ter- 
mination of  each  branch,  where  the  mouth  and  tentacles 
are  located.  In  certain  species — for  example,  the  sea  pens 
(Pennatula)  and  sea  fans  (Gorgonid) — a  skeleton  may  be 


FIG.  26.— Small  portions  of 


with  some  of  the  polyps  expanded. 


formed  of  myriads  of  lime  spicules,  somewhat  like  those 
of  the  sponge,  which  are  bound  together  by  the  fleshy 
substance  of  the  body;  but  the  skeleton  of  most  of  the 
common  forms  in  the  ocean,  and  the  coral  found  in 
general  collections,  is  stony.  According  to  their  method 
of  branching,  such  specimens  have  received  various  popu- 
lar names,  such  as  brain,  stag-horn,  organ-pipe,  and  fun- 
gous corals. 


THE  CCELENTEEATES  43 

Nearly  all  species,  like  the  sea-anemones,  are  brilliantly 
colored  during  life,  and  several  are  highly  phosphorescent. 
All  are  marine,  and  while  they  are  found  everywhere,  from 
the  shore-line  to  great  depths,  the  more  abundant  and 
larger  species  inhabit  the  clear,  warm  waters  of  the  tropics 
down  to  a  depth  of  one  hundred  and  sixty  feet.  In  such 
regions  the  stag-horn  corals  especially  grow  in  the  wildest 
profusion,  and  become  tall  and  greatly  branched.  Except 
in  quiet  water  they  are  continually  being  broken  by  the 
waves,  beaten  into  fragments,  and  the  resulting  sand  is 
deposited  about  their  bases.  As  a  result  of  this  continu- 
ous growth  and  erosion,  there  have  been  formed  from  coral 
sand  mixed  with  the  shells  of  mollusks  and  the  skeletons 
of  various  Protozoa  several  of  the  islands  along  the  Florida 
coast  and  many  of  those  of  the  Pacific,  some  of  them 
hundreds  of  miles  in  extent. 


CHAPTER  VI 

THE    WORMS 

42.  General  Characteristics.— The  bodies  of  the  animals 
comprising  the  two  preceding  groups  are  exposed  on  all 
sides  equally  to  the  water  in  which  they  live  and  are  radi- 
ally symmetrical ;  but  in  the  worms,  one  side  of  the  body 
is  fitted  for  creeping,  and  for  the  first  time  we  note  a  well- 
marked  dorsal  (back)  and  ventral  (under)  surface.  In  the 
former,  the  body,  like  a  cylinder,  may  be  divided  into  simi- 
lar halves  by  any  number  of  planes  passing  lengthwise 
through  the  middle ;  but  in  the  worms,  the  right  and  left 
halves  only  are  exposed  equally  to  their  surroundings,  and 
there  is,  accordingly,  only  one  plane  which  divides  the  body 
into  corresponding  halves,  so  that  these  animals,  like  all 
higher  forms,  are  bilaterally  symmetrical.  In  creeping,  also, 
one  end  of  the  body  is  directed  forward  and  it  thus  be- 
comes correspondingly  modified.  It  usually  bears  the 
mouth,  and  may  be  provided  with  eyes,  feelers,  or  organs 
of  touch,  and  various  other  structures  which  enable  the 
worm  to  recognize  the  nature  of  its  surroundings.  The 
nervous  and  muscular  systems  are  better  developed  than  in 
the  foregoing  groups,  and  we  note  a  greater  vigor  and  defi- 
niteness  in  the  animal's  movements,  and  in  various  ways  the 
worms  appear  better  able  to  avoid  or  ward  off  their  enemies, 
recognize  and  select  their  food,  and  in  general  adapt  them- 
selves to  the  conditions  of  life. 

The  division  of  the  worms  is  a  very  large  one,  and  in 
some  respects  difficult  to  define,  owing  to  the  close  resem- 
44 


THE  WORMS 


45 


blance  which  many  of  them  show  to  animals  in  other 
groups.  All  the  invertebrates,  therefore,  except  the  crabs 
and  insects,  were  placed  in  one  group  until  subsequent 
study  made  it  possible  to  classify  them  more  exactly.  Ac- 
cording to  the  general  shape  of  the  body,  and  the  arrange- 
ment of  internal  organs,  worms  are  divided  into  a  number 
of  groups,  chief  among  which  are  the  flatworms,  the  thread 
or  roundworms,  and  the  ringed  worms  or  annelids. 

THE  FLATWORMS 

43.  Form  and  habitat. — The  flatworms,  as  their  name 
indicates,  are  much  flattened,  leaf-like  forms,  some  species 
living  in  damp  places  on  land, 
in  fresh  -  water  streams  or 
ponds,  or  along  the  seacoast, 
while  a  variety  of  other  spe- 
cies are  parasitic.  The  free 
forms  (Fig.  27)  are  usually 
small,  barely  reaching  a  length 
greater  than  five  or  seven  cen- 
timeters (2  to  3  inches),  but 
some  of  the  parasitic  species 
(Fig.  31)  attain  the  great 
length  of  six  to  thirteen  me- 
ters (20  to  40  feet). 

The  free-living  forms  usu- 
ally occur  on  the  under  side 
of  stones,  and  frequently  are 
so  delicate  that  a  touch  is 
sufficient  to  destroy  them.  A 

few   Species   are   almost   trans-    FIG.  27.-A,  fresh-water  flatworm  (Pla- 
.  naria) ;  B,  marine  flatworm  (Lepto- 

parent,  while  many  are   col-       ^ana)    Enlarged,  from  Nature. 
ored  to  harmonize  completely 

with  their  surroundings,  so  that,  even  though  fragile  and 
defenseless,  they  escape  the  attacks  of  enemies  by  being 
overlooked.  The  night-time  or  dark  days  are  their  hunting 


46 


ANIMAL   FORMS 


season,  and  at  such  periods  they  may  be  found  moving  about 
with  a  steady  gliding  motion  (due  to  cilia  covering  the  en- 
tire body),  varied  occasionally  by  a  looping,  caterpillar  move- 
ment, or  by  swimming  with  a  napping  of  the  sides  of  the 
body.  When  watched  at  such  times  they  may  sometimes 
be  seen  to  snatch  up  small  worms,  snails,  small  crabs  and 
insects,  which  serve  as  food. 

More  closely  examining  one  of  these  forms,  for  example, 
the  species  usually  found  on  the  under  side  of  sticks  and 
stones  in  our  shallow  fresh-water  streams  (Fig.  27,  A),  we  note 
that  the  forward  end  is  not  developed  into  a  well-defined 
head  as  in  the  higher  worms, 
but  is  readily  determined  by 
the  presence  of  very  simple 
eyes  and  tentacles,  while  the 
lower  creeping  surface  is  dis- 
tinguished by  a  lighter  color 
and  the  presence  of  the 
mouth.  Through  this  small 
opening  a  slender  proboscis 
(in  reality  the  pharynx)  may 
be  extended  some  distance, 
and  may  be  seen  to  hold  the 
small  organisms  upon  which 
it  lives  until  they  are  suffi- 
ciently digested  to  be  taken 
into  the  body. 

44,  Digestive  system. — In 
the  smaller  flatworms,  some 
of  which  are  scarcely  larger 
than  many  of  the  Protozoa, 
the  alimentary  canal  is  a  sim- 
ple unbranched  tube ;  but  in 
the  larger  forms  such  an  ap- 
paratus is  replaced  by  a  greatly  branched  digestive  tract 
which  furnishes  an  extensive  surface  for  the  rapid  absorp- 


FIG.  28.— Anatomy  of  fresh-water  flat- 
worm  (Planaria).  exs,  excretory  sys- 
tem, with  flame-cell  (/).  The  ali- 
mentary canal  is  stippled.  B,  nerv- 
ous system. 


THE   WORMS 


47 


tion  of  food,  and  extending  deep  into  the  tissues  of  the 
body,  carries  nutriment  to  otherwise  isolated  regions.     In 
the  fresh-water  forms  and  their  allies  there  are  three  main 
branches  of  the  intestine  (Fig.  28),  while  in  many  of  those 
from  the  sea  there   are   several,  and  their  arrangement 
affords  a  basis  for  their  general  classification. 
•    45.  Excretory  system. — In  the  sponges  and  ccelenterates 
the  wastes  are  cast  out  by  the  various  cells  into  the  gastric 
cavity  or  at  once  to  the  exterior  with- 
out the  aid  of  any  pronounced  system 
of  vessels;  but  in  the  flatworms  sev- 
eral of  the  organs  are  deeply  buried 
within  the  tissues  of  the  body  and  a 
drainage  system  becomes  a  necessity. 
This  consists  of  a  paired  system  of  ves- 
sels extending  the  length  of  the  ani- 
mal (Fig.  28)  and  provided  with  numer- 
ous branches,  some  of  which  open  at 
various  points  on  the  surface  of  the 
body,  while  the   others   terminate  in 
spaces  (Fig.  29,  s)  among  the  organs  in 
what  are  known  as  flame-cells.     The 
substances  which  accumulate  in  these 
spaces  are  gathered  up  by  the  flame- 
cell,  poured  into  the  space  it  contains,  and  by  means  of  the 
vibratory  motion  of  its  flagellum  (/),  a  movement  bearing 
a  fancied  resemblance  to  the  flickering  of  a  flame  in  the 
wind,  are  borne  through  the  tubes  to  the  exterior. 

46.  Nervous  system  and  sense-organs. — In  the  sponges  no 
definite  nervous  system  is  known  to  exist,  the  slight  move- 
ments which  the  cells  are  able  to  undergo  being  regulated 
somewhat  as  they  are  in  the  Protozoa.  Among  the  ccelen- 
terates certain  of  the  cells  scattered  over  the  surface  of  the 
body  are  set  aside  as  nerve-cells,  and,  more  or  less  united  by 
means  of  fibers  extending  from  them,  convey  impulses  over 
the  body.  In  the  flatworms  the  larger  number  of  nerve-cells 


FIG.  29.— Flame-cell  of  flat- 
worm  (after  LANG).  /, 
flagellum  ;  n,  nucleus; 
s,  spaces  among  the  or- 
gans of  the  body  ;  v, 
waste  materials. 


48  ANIMAL   FORMS 

are  collected  into  two  definite  masses  (Fig.  28,  B),  which 
constitute  a  simple  brain  on  which  the  eyes  are  situated 
and  from  which  bundles  of  nerve  fibers  pass  to  all  parts  of 
the  body,  the  two  extending  backward  being  especially 
noticeable.  As  in  the  squirrel,  these  are  distributed  to  the 
muscles  and  other  organs  to  regulate  their  activity,  while 
those  distributed  to  the  skin,  especially  in  the  forward 
part  of  the  body,  convey  stimuli  produced  by  touch.  The 
branches  connecting  with  the  eyes  enable  the  animal  to 
distinguish  light  from  darkness,  but  are  probably  too  sim- 
ple to  allow  it  to  clearly  distinguish  objects  of  the  outside 
world.  The  sense  of  smell  and  possibly  that  of  taste  are 
also  present,  but  are  relatively  feeble. 

Some  other  characters  of  this  class  will  be  noted  in  the 
consideration  of  the  two  following  classes. 

47.  Parasitic  flatworms  (trematodes)— parasitism.— Men- 
tion has  already  been  made  of  the  associations  of  two  ani- 
mals as  "  messmates "  for  mutual  benefit,  such  as  the  Hy- 
dractinia  growing  on  the  surface  of  the  shell  inhabited  by 
the  hermit  crab,  to  which  it  gives  protection  by  means  of 
its  nettle-cells,  while  in  turn  being  borne  continually  into 
regions  abounding  with  food.  More  frequently,  however, 
one  animal  derives  benefit  from  another  without  making 
any  compensation.  For  example,  many  species  of  flatworms 
live  within  the  shells  of  certain  snails  and  upon  the  bodies 
of  sea-urchins  and  starfishes,  where  they  gather  in  their 
food  supply  safe  from  the  attacks  of  enemies.  Such  asso- 
ciations are  probably  without  much  if  any  inconvenience  to 
the  animal  thus  inhabited,  and  it  also  appears  probable 
that  the  tenants  are  transients,  using  the  mollusk  or  star- 
fish only  as  a  temporary  home.  But  from  this  condition  of 
affairs  it  is  only  a  short  step  to  the  parasitic  habit,  where 
the  association  becomes  permanent  and  the  occupant  is 
provided  with  various  structures  which  prevent  its  sepa- 
ration from  its  host.  This  latter  kind  of  union  occurs 
throughout  the  group  of  trematodes ;  all  are  parasitic,  and 


THE   WORMS 


their  internal  organization,  so  closely  resembling  that  of 
the  free-living  forms  as  to  need  no  further  description,  in- 
dicates that  they  are 
descendants  of  the  lat- 
ter. In  the  greater 
number  the  body  is 
flat,  and  a  few  species 
still  retain  their  outer 
coat  of  cilia  ;  but  since 
these  are  no  longer  of 
service  as  locomotor 
organs  they  have  gen- 
erally disappeared,  and 
in  their  place  numer- 
ous adhesive  organs, 
such  as  spines,  hooks, 
and  suckers  (Fig.  30), 
have  arisen,  which  en- 
able the  animals  to 
hold  on  with  great  te- 
nacity. Thus  attached 
to  its  host,  and  using 
it  as  a  convenient  and 
comparatively  safe 
means  of  locomotion, 
the  parasite  may  still 

continue  to  capture  small  animals  for  food  or  may  derive 
its  nourishment  from  the  tissues  of  the  host.  In  addition 
there  are  numbers  of  internal  parasites,  living  almost  ex- 
clusively in  the  bodies  of  vertebrate  animals,  scarcely  a  sin- 
gle one  escaping  their  ravages. 

48.  Life  history. — In  the  external  parasites  the  young 
hatch  out  and  with  comparative  ease  make  their  way  to 
another  host ;  but  the  young  of  an  internal  parasite,  inhab- 
iting the  alimentary  canal,  have  a  very  slight  chance  in- 
deed of  ever  reaching  a  similar  location  in  another  host. 


FIG.  30.  —  A  parasitic  flatworm  (Epidetta).  m 
mouth  ;  o,  opening  of  reproductive  system  ; 
«,  sucker  and  spines  for  attachment.  The  di- 
gestive system  is  stippled  ;  nervous  system 
black.  Enlarged  8  times,  from  Nature. 


50  ANIMAL  FORMS 

For  this  reason  an  almost  incredible  number  of  eggs  is  laid, 
and  some  extraordinary  measures  are  employed  in  effecting 
the  desired  result.  Probably  the  best-known  example  is  that 
of  the  liver  fluke  inhabiting  the  bile-ducts  in  the  sheep. 
Each  worm  lays  several  hundred  thousand  eggs,  which  make 
their  way  from  the  host,  and  if  they  chance  to  fall  in  pools 
of  water  or  damp  situations  may  proceed  to  develop,  other- 
wise not.  If  the  surroundings  be  favorable,  the  young,  like 
little  ciliated  Infusoria,  escape  from  their  shells  and  rest- 
lessly swim  or  move  about  for  a  short  time,  and  if  during 
this  time  they  come  in  contact  with  certain  species  of 
snails  living  in  these  situations  they  at  once  bore  into  their 
bodies.  Here  they  produce  other  young  somewhat  resem- 
bling a  tadpole,  that  now  make  their  escape  from  the  snail. 
In  a  short  time  each  one  crawls  upon  a  blade  of  grass,  and 
surrounds  itself  with  a  tough  shell,  where  it  may  remain  for 
several  weeks.  If  the  grass  on  which  they  rest  be  eaten  by 
a  sheep,  they  finally  make  their  way  to  the  bile-ducts  and 
there  become  adult.  The  life  cycle  is  now  complete ;  the 
young  form  has  found  a  new  host ;  and  the  process  shows 
how  wonderfully  animals  are  adapted  to  the  conditions  which 
surround  them,  and  how  closely  they  must  conform  to  these 
conditions  in  order  to  exist. 

49.  The  tapeworms  (cestodes). — The  cestodes,  or  tape- 
worms, are  also  parasitic  flatworms  in  which  the  effects  of 
such  a  mode  of  life  are  strongly  marked.  They  occur 
almost  exclusively  in  the  bodies  of  vertebrate  hosts  and 
exhibit  a  great  variety  of  bodily  forms,  in  some  cases  resem- 
bling rather  closely  the  trematodes,  but  in  others  strikingly 
different.  In  the  latter  type  the  body  is  usually  of  great 
length  (from  a  few  centimeters  to  upwards  of  sixteen  meters 
(50  feet) ),  and  terminates  in  a  "head"  (Fig.  31)  provided, 
in  the  different  species,  with  a  great  variety  of  hooks  and 
spines  and  numbers  of  suckers  for  its  attachment  to  the 
body  of  the  host.  From  the  head  the  body  extends  back- 
ward in  the  gradually  enlarging  ribbon-like  body,  slender  at 


THE   WORMS 


51 


first  and  scarcely  showing  the  segments  which  finally  be- 
come so  prominent  a  feature. 

When  carefully  examined,  a  two-lobed  brain  is  found 
in  the  "  head,"  and  from  it  nerves  extend  the  entire  length 
of  the  body,  followed  throughout  their 
course  by  the  tubes  of  the  excretory 
system ;  also  each  segment  contains  a 
perfect  reproductive  system,  so  that 
even  if  it  be  separated  from  the  others 
it  may  continue  to  exist  for  a  consid- 
erable length  of  time.  Furthermore, 
the  tapeworms  are  surrounded  by  the 
predigested  fluids  of  their  host ;  a 
special  alimentary  canal  is  therefore 
superfluous,  and  all  traces  of  it  have 
disappeared. 

50.  Development. — As   the  animal 
clings  in  this  passive  way  to  the  body 
of  its  host  the  segments,  loaded  with 
eggs  ready  for  development,  separate 
one  after  another  from  the  free  end 
of  the  body,  pass  to  the  exterior,  and 

slowly  crawling  about  like  independent  organisms,  lay  great 
numbers  of  eggs,  which  may  find  an  intermediate  host  as  in 
the  life  cycle  of  the  liver  fluke,  and  so  in  time  find  their 
permanent  resting-place.  Fortunately  in  all  these  parasitic 
forms,  though  an  inconceivably  great  number  of  eggs  are 
laid,  only  a  comparatively  few  reach  maturity.  Even  these, 
however,  may  cause  at  times  great  destruction  among  the 
higher,  and  especially  our  domestic,  animals,  often  doing 
damage  amounting  to  many  millions  of  dollars  per  year. 

51.  The  tapeworm  in  relation  to  regeneration. — It  has 
been  known  for  more  than  one  hundred  and  fifty  years  that 
some  of  the  lower  animals  possess  to  a  surprising  degree 
the  ability  to  regenerate  parts  of  the  body  lost  through 
injury.     The  Hydra,  hydroids,  and  some  of  the  jelly-fishes 


PIG.  31. — Tapeworm  (Tcenia 
solium).  In  upper  left- 
hand  corner  of  figure  is 
the  much  enlarged  head. 
—After  LEUCKART. 


52  ANIMAL   FORMS 

may  be  cut  into  a  number  of  pieces,  each  of  which  will 
develop  into  a  complete  individual ;  and  this  power  of  recov- 
ery from  the  injuries  produced  by  enemies  is  of  the  great- 
est service  in  the  perpetuation  of  the  species.  This  ability 
is  also  present  in  certain  flatworms,  and  some  species  are 
known  which  voluntarily  separate  the  body  into  two  por- 
tions, each  of  which  becomes  an  adult.  In  other  species  a 
similar  process  results  in  the  formation  of  a  chain  of  six 
individuals,  placed  end  to  end,  the  chain  finally  breaking 
up  into  as  many  complete  worms.  It  is  possible  that  the 
tapeworm  may  also  be  looked  upon  as  a  great  chain  of 
united  individuals  produced  by  the  division  of  a  single 
original  parent,  which  becomes  adapted  for  attaching  the 
others  until  they  separate.  These  latter  are  capable  only  of 
a  very  sluggish  movement,  and,  devoid  of  mouth  and  ali- 
mentary canal,  are  not  able  to  digest  their  food,  but  their 
life  work  is  to  so  lay  their  eggs  that  they  may  develop  into 
other  individuals,  and  for  this  they  are  well  adapted. 

NEMATODES  (THREADWORMS) 

52.  General  characters. — This  class  of  worms  is  com- 
posed of  an  enormous  number  of  different  species,  some  para- 
sitic, others  free  all  or  a  portion  of  their  lives,  and  in  view  of 
the  fact  that  they  inhabit  the  most  diverse  situations  it  is 
remarkable  that  they  are  so  uniform  in  their  structure.  In 
all  the  body  is  slender,  and  the  general  features  of  its  organ- 
ization may  be  readily  understood  from  an  examination  of 
the  "vinegar  eel"  (Fig.  32,  A).  This  small  worm  (not  an 
eel),  a  millimeter  or  two  in  length,  lives  on  the  various  forms 
of  mold  that  grow  in  fermenting  fruit  juices,  especially 
after  a  little  sugar  or  paste  has  been  added.  A  tough  cuti- 
cle surrounds  the  body,  preserving  its  shape  and  at  the 
same  time  protecting  the  delicate  organs  against  the  action 
of  the  acids  in  which  it  lives.  Through  this  may  be  seen 
great  bands  of  muscles  extending  the  entire  length  of  the 
body  and  producing  the  wriggling  movements  of  swimming 


THE  WORMS 


53 


or  crawling.  They  also  give  support  to  a  brain,  which  is  in 
the  form  of  a  collar  encircling  the  pharynx  near  the  head, 
and  to  the  great  nerves  which  extend  from  it.  Still  fur- 
ther within  the  transparent  body  the  alimentary  canal  may 
be  distinguished  as  a  straight  tube 
passing  directly  through  the  ani- 
mal. This  latter  system  lies  freely 
in  a  great  space,  the  body  cavity, 
traces  of  which  may  exist  in  the 
flatworms  in  the  form  of  small  hol- 
lows among  the  organs  into  which 
the  kidneys  open.  It  is  possible 
that  in  this  form  also  the  kidneys 
open  into  this  space,  and  it  is 
roomy  enough  besides  to  afford 
lodgment  for  the  reproductive  or- 
gans in  addition  to  a  large  amount 
of  fluid  which  is  probably  somewhat 
of  the  nature  of  blood.  A  space  in 
some  respects  similar  to  this  occurs 
in  all  the  animals  above  this  group, 
and  as  we  shall  see,  it  is  often  cu- 
riously modified  and  serves  for  a 
number  of  different  and  highly  im- 
portant purposes.  In  the  round- 
worms  the  fluid  it  contains  proba- 
bly acts  in  the  nature  of  a  blood 
system,  distributing  the  food  and 
oxygen  to  various  parts  of  the  body  and  carrying  the  wastes 
to  the  kidneys  for  removal. 

53.  Multiplication.— In  the  matter  of  the  production  of 
new  individuals  the  greatest  differences  exist.  In  some 
threadworms,  for  example  the  "  vinegar  eel,"  eggs  develop 
within  the  body  and  the  young  are  born  with  the  form  of  the 
parent.  In  other  cases  the  eggs  are  laid  in  the  water,  where 
they,  too,  may  directly  grow  to  the  adult  condition  ;  but  in 


FIG.  32.  —  Thread-  or  round- 
worms.  A,  vinegar  eel  (An- 
guittula) ;  m,  mouth  ;  ph., 
pharynx  ;  i,  intestine  ;  ov., 
developing  young.  B,  TH- 
china.  From  Nature,  greatly 
enlarged. 


54  ANIMAL  FORMS 

the  greater  number  of  species  the  development  is  round- 
about, and  one  or  more  hosts  are  inhabited  before  the  young 
assume  the  adult  condition.  Such  is  the  case  with  the 
dreaded  Trichina  (Fig.  32,  B),  which  infests  the  bodies  of 
several  animals,  particularly  the  rat.  When  these  forms 
are  introduced  into  the  alimentary  canal  of  the  rat,  for 
example,  they  soon  lay  a  vast  quantity  of  eggs,  sometimes 
many  millions,  which  develop  into  young  that  bore  their 
way  into  the  muscles  of  the  body,  where  they  may  remain 
coiled  up  for  years.  If  the  body  of  the  rat  be  eaten  by  some 
carnivorous  animal,  these  excessively  small  young  are  lib- 
erated during  the  process  of  digestion  and  rapidly  assume 
the  adult  condition  in  the  alimentary  canal,  likewise  giving 
rise  to  young  which  pursue  again  this  same  course  of 
development. 

Another  example  of  a  complicated  life  history  is  in 
the  Gordius  or  "  horsehair  snake  "  (a  true  worm  and  not  a 
snake)  frequently  seen  in  the  spring  in  pools  where  it  lays 
its  eggs.  These  eggs  develop  into  young  which  bore  their 
way  into  different  insect  larva?,  which  are  in  turn  eaten  by 
some  spider  or  beetle,  and  the  worm  thus  transferred  to  a 
new  host.  In  this  they  grow  to  a  considerable  size,  and 
then  make  their  exit  from  the  body  of  the  host  and  finally 
become  adult. 

54.  Spontaneous  generation. — It  is  only  within  compara- 
tively recent  years  that  such  life  histories  have  been  under- 
stood. Formerly  the  sudden  appearance  of  these  and  other 
forms  in  various  situations  were  accounted  for  on  the  ground 
that  they  arose  spontaneously  without  the  intervention  of 
any  living  creature.  Even  yet  we  hear  of  the  transforma- 
tion of  horsehairs  into  hairworms,  and  of  frogs,  earthworms, 
and  several  other  animals  from  inorganic  matter,  but  such 
assertions  are  based  on  superficial  observations,  and  at  the 
present  time  no  exception  is  known  to  the  law  that  living 
creatures  arise  from  preexisting  living  parents.  "  All  life 
from  life  "  (omnium  vivum  ex  vivo)  is  a  universal  law. 


THE   WORMS  55 


ANNELIDS  OK  SEGMENTED  WORMS 

55.  The  earthworms  and  their  relatives.— Leaving  the 
groups  of  the  parasitic  animals,  which  have  been  driven  from 
the  field  of  active  existence  and  in  many  ways  are  degraded 
by  such  a  mode  of  life,  we  pass  on  to  the  higher  free-living 
worms,  where  brilliant  colors,  peculiar  habits,  or  remarkable 
adaptations  render  them  peculiarly  interesting.  In  consid- 
ering first  their  general  organization,  we  may  use  the  earth- 


FIG.  33. — Earthworm  (Lumbrlcus  terrestris).    m,  mouth  ;  c,  girdle  or  clitellum. 

worm  (Fig.  33)  (sometimes  called  angle-worm  or  fish-worm) 
as  a  type  because  of  its  almost  universal  distribution. 

The  body  is  cylindrical,  shows  well-marked  dorsal  and 
ventral  surfaces,  and,  as  in  all  of  the  annelids,  is  jointed, 
each  joint  being  known  as  a  segment.  Anteriorly  it  tapers 
to  a  point,  and  the  head  region  bearing  the  mouth  is  ill- 
defined,  unlike  many  sea  forms,  yet  serves  admirably  for 
tunneling  the  soil  in  which  all  earthworms  live.  In  this 
process  the  animal  is  also  aided  by  bristles  or  setce  which 
project  from  the  body  wall  of  almo'st  every  segment  and 
may  be  stuck  into  the  earth  to  afford  a  foothold. 

56.  Foodjmd  digestive  system. — The  earthworms  are 
nocturnal  animals,  seldom  coming  to  the  surface  during  the 
day  except  when  forced  to  do  so  by  the  filling  of  their  tun- 
nels with  water  or  when  pursued  by  enemies.  At  night 
they  usually  emerge  partially,  keeping  the  posterior  end  of 
the  body  within  the  burrow,  and  thus  they  scour  the  sur- 
rounding areas  for  food,  which  they  appear,  in  some  cases 
at  least,  to  locate  by  a  feeble  sense  of  smell.  They  also 
frequently  extend  their  habitations,  and  in  so  doing  swallow 
enormous  quantities  of  earth  from  which  they  digest  out 
any  nutritive  substances,  leaving  the  indigestible  matter  in 
5 


5G  ANIMAL    FORMS 

coiled  "  castings  "  at  the  entrance  of  the  burrows.  In  thus 
mixing  the  soil  and  rendering  it  porous  they  are  of  great 
service  to  the  agriculturist. 

Although  earthworms  are  omnivorous  they  also  manifest 
a  preference  for  certain  kinds  of  food,  notably  cabbage, 
celery,  and  meat,  which  leads  us  to  think  that  they  have  a 
sense  of  taste.  All  these  substances  are  carried  within  their 
retreats  and  devoured,  or  are  used  to  block  the  entrance 
during  the  day.  The  food  thus  carried  within  the  body  is 
digested  by  a  system  (Fig.  34)  composed  of  several  portions, 


FIG.  34.— Earthworm  ( Lwtnbricus)  dissected  from  left  side,  b,  brain;  c,  crop;  rf, 
outer  opening  of  male  reproductive  system  ;  dr,  dorsal  blood-s-essel :  g.  gizzard  : 
h,  pulsating  vessels  or  •'  hearts  "  ;  i,  intestine  ;  k,  kidney  ;  »»,  month  ;  n.  c..  nerve- 
cord  ;  oe,  esophagus  ;  o,  ovary  ;  od,  oviduct :  ph.  pharynx  ;  r,  testes :  g.r..  sem- 
inal receptacles  ;  v.v.,  ventral  vessel. 

each  of  which  is  modified  for  a  particular  part  in  the  pro- 
cess. The  mouth  (m)  leads  into  a  muscular  pharynx  (ph) 
whose  action  enables  the  worm  to  retain  its  hold  on  various 
objects  until  swallowed,  and  this  in  turn  is  continuous  with 
the  esophagus.  From  here  the  food  is  passed  into  the  thin- 
walled  crop  (c),and  from  this  storehouse  is  gradually  borne 
into  the  gizzard  (#),  whose  muscular  walls  reduce  it  to  a  fine 
pulp  now  readily  acted  upon  by  the  digestive  fluids.  These, 
resembling  in  their  action  the  pancreatic  juice  of  higher 
animals,  are  poured  out  from  the  walls  of  the  intestine  into 
which  the  food  now  makes  its  way ;  and  as  it  courses  down 
this  relatively  simple  tube  the  nutritive  substances  are  ab- 
sorbed while  the  indigestible  matters  are  cast  away. 

57.  Circulatory  system. — In  all  the  groups  of  animals  up 
to  this  point  the  digested  food  is  carried  over  the  body  by 
a  simple  process  of  absorption,  or  in  the  threadworms  by 


THE   WORMS 


57 


means  of  the  fluid  in  the  body  cavity  ;  but  in  the  earthworm 
the  division  of  labor  between  different  parts  of  the  body  is 
more  perfect,  and  a  definite  blood  system  now  acts  as  a 
distributing  apparatus.  This  consists  primarily  of  a  dorsal 
vessel  lying  along  the  dorsal  surface  of  the  alimentary  canal 
(Fig.  34),  from  which  numerous  branches  are  given  off  to 
the  body  wall,  and  to  the  digestive  system  through  which 
they  ramify  in  every  direction  before  again  being  collected 
into  a  ventral  vessel  lying  below  the  digestive  tract.  In 
some  of  the  anterior  segments  a  few  of  the  connecting 
vessels  are  muscular  and  unbranched,  and  during  life  pul- 
•sate  like  so  many  hearts  to  force  the  blood  over  the  body, 
forward  in  the  dorsal  vessel,  through  the  "  hearts  "  into  the 
ventral  vessel,  thence  into  the  dorsal  by  i  • 

means  of  the  small  connecting  branches. 

Some  of  the  duties  of  this  vascular 
system  are  also  shared  by  the  fluid  of 
the  body  cavity,  which  is  made  to  cir- 
culate through  openings  in  the  parti- 
tions by  the  contractions  of  the  body 
wall  of  the  animal  in  the  act  of  crawl- 
ing. In  this  rough  fashion  a  consider- 
able amount  of  nutritive  material  and 
oxygen  are  distributed  to  various  or- 
gans, and  wastes  are  carried  to  the  kid-  FlG  35 
neys  to  be  removed. 

58.  Excretion. — In  nearly  all  of  the 
segmented  worms  there  is  a  pair  of 
kidneys  to  every  segment  (Figs.  34,  35). 
Each  consists  of  a  coiled  tube  wrapped  in  a  mass  of  small 
blood-vessels,  and  at  its  inner  end  communicating  with  the 
body  cavity  by  means  of  a  funnel-shaped  opening.  In 
some  unknown  way  the  walls  of  the  kidney  extract  the 
waste  materials  from  the  blood-vessels  coursing  over  it  and 
pass  them  into  its  tubular  cavity.  At  the  same  time  the 
cilia  about  the  mouth  of  the  funnel-shaped  extremity  are 


Diagram  of  earth- 
worm kidney.  6,  blood- 
vessel ;  /,  funnel  open- 
ing into  body  cavity ; 
o,  outer  opening ;  «, 
septum  ;  w,  body  wall. 


58  ANIMAL  FORMS 

driving  a  current  from  the  body-cavity  fluids,  which  wash 
the  wastes  to  the  exterior. 

59.  Nervous  system. — The  nervous  system  of  the  earth- 
worm consists  first  of  a  brain  composed  of  two  pear-shaped 
masses  united  together  above  the  pharynx  (one  shown  in 
Fig.  34),  from  which  nerves  pass  out  to  the  upper  lip  and 
the  head,  which  are  thus  rendered  highly  sensitive.     Two 
other  nerves  also  pass  out  from  the  brain,  and,  coursing 
down  on  each  side  of  the  pharynx  like  a  collar,  unite  below 
it  and  extend  side  by  side  along  the  under  surface  of  the 
digestive   system  throughout  its  entire  extent.     In  each 
segment  the  two  halves  of  this  ventral  nerve-cord  are  united 
by  a  nerve,  and  others  are  distributed  to  various  organs, 
which«are  thus  made  to  act  and  in  proper  amount  for  the 
good  of  the  body  as  a  whole. 

In  its  relation  to  the  outside  world  the  chief  source  of 
information  comes  to  the  earthworm  through  the  sense  of 
touch,  for  definite  organs  of  sight,  taste,  and  smell  are  but 
feebly  developed,  while  ears  appear  to  be  entirely  absent. 
Nevertheless  these  are  sufficient  to  enable  it  to  lead  a  suc- 
cessful life,  as  is  evidenced  by  the  great  number  of  such 
forms  found  on  every  hand. 

60.  Egg-laying. — In  digging  up  the  soil  where   earth- 
worms  abound   one   frequently   finds   small  yellowish    or 
brownish  bodies  looking  something  like  a  grain  of  wheat. 
These  are  the  cocoons  in  which  the  earthworms  lay  their 
eggs,  and  the  method  by  which  this  is  performed  is  unique. 
We  have  already  noted  the  presence  of  a  swollen  girdle 
(the  clitellum]  about  the  body  of  the  worm.     At  the  breed- 
ing season  this  throws  out  a  fluid  which  soon  hardens  into 
an  encircling  band.     By  vigorous  contractions  of  the  body 
this  horn-like  collar  is  now  slipped  forward,  and  as  it  passes 
the  openings   of  the  reproductive   organs  the   eggs  and 
sperms  are  pushed  within  it.     They  thus  occupy  the  space 
between  the  worm  and  the  collar,  and  when  the  latter  is 
shoved  off  over  the  head  its  ends  close  as  though  drawn  to- 


THE   WORMS 


50 


gether  by  elastic  bands.     A  sac,  the  cocoon,  is  thus  pro- 
duced, containing  the  eggs  and  a  milky,  nutritive  substance. 
In  a  few  weeks  the  worm 
develops  and,  bursting  the 
wall  of  its  prison,  makes  its 
escape. 

61.  Distribution.  —  The 
earthworms  and  their  allies 
are  found  widely  distributed 
throughout  the  world,  and 
all   exhibit    many    of    the 
characters    just    described. 
The     greatest     differences 
arise  in  their  mode  of  life  : 
some  are  truly  earthworms, 
but  others  are  fitted  for  a 
purely  aquatic  existence  in 
fresh    water   or   along    the 
seacoast ;  a  few  have  taken 
up  abodes   in   various  ani- 
mals   and    plants,   and    in 
some  of  these  situations  they 
extend  far  up  the  sides  of 
the  higher  mountains.     In 
all,  the  head   is   relatively 
indistinct,    the    number   of 

bristles     OU     each      segment    Fl«-  36.— A  marine  worm  (Nereis).    A,  ap- 

few,  and  for  this  and  other        j;~  mes^"8  """*'  "*  * 

reasons  all  are  included  in 

the  subclass  Oligochaste,  or  "  few-bristle  "  worms. 

62.  Nereis  and  its  allies. — In  many  of  the  above-men- 
tioned situations  members  of  a  more  extensive  group  of 
worms  are  found,  with  highly  developed  heads  and  many 
bristles  arranged  along  the  sides  of  the  body.     These  are 
the  Polychaetes  or  "  many-bristle  "  worms,  and  as  a  repre- 
sentative we  may  take  Nereis  (Fig.  36),  a  very  common 


60 


ANIMAL   FORMS 


form  along  almost  any  seashore.  The  body  presents  the 
same  segmented  appearance  as  the  earthworm,  but  the 
head  (Fig.  37,  A)  is  provided  with  numerous  sense  organs, 
chief  among  which  are  four  eyes  and 
several  tentacles  or  "  feelers." 

The   segments  behind  the    head 


FIG.  37.— A.  head  and  one  of  the  lateral  appendages  (B)  of  a  marine  worm  (Nereis 
brandtii) ;  al.  intestine  ;  /,  "  gill  "  ;  k,  kidney  ;  n,  nerve  cord  ;  s,  bristles  for  loco- 
motion. 

differ  very  little  from  one  another,  and,  unlike  those  of 
the  earthworm,  each  bears  a  pair  of  lateral  plates  (Figs. 
36,  37,  B)  or  paddles  with  many  lobes,  some  of  which  bear 
numerous  bristles.  By  a  to-and-f  ro  movement  these  organs 
aid  in  pushing  the  animal  about,  or  may  enable  certain  spe- 
cies to  swim  with  considerable  rapidity. 

As  in  all  other  worms,  respiration  takes  place  through 
the  surface  of  the  body,  the  area  of  which  is  increased  by 
the  development,  on  certain  portions  of  the  paddles  (para- 
podia),  of  plates  penetrated  with  numerous  blood-vessels, 
which  thus  become  special  respiratory  organs  or  gills 
(Fig.  37,  B). 

In  their  internal  organization  the  Polychaetes  are  con- 
structed practically  on  the  same  plan  as  the  earthworms, 
the  principal  difference  being  in  the  reproductive  system. 
In  the  earthworm  this  is  restricted  to  some  of  the  forward 
segments,  while  in  the  present  group  the  eggs  and  sperms 


THE  WORMS 


fit 


are  developed  in  almost  every  segment,  whence  they  are 
finally  swept  to  the  exterior  through  the  tubes  of  the  kid- 
neys (Fig.  37,  B). 

The  Nereis  and  its  immediate  relatives  are  all  active 
forms,  and  by  means  of  powerful  jaws,  which  may  be  quickly 
extended  from  the  lower  part  of  the  mouth  cavity,  they 
capture  large  numbers  of  small  crustaceans,  mollusks,  and 
worms  which  happen  in  their  path.  Others  more  distantly 
related  make  their  diet  of  seaweed,  and 
many  living  on  the  sea  bottom  swallow 
great  quantities  of  sand,  from  which  they 
absorb  the  nutritious  substances. 

63.  Sedentary  forms. — Preyed  upon  by 
many  enemies,  a  large  number  of  species 
have  been  forced  to  abandon  an  active  ex- 
istence save  in  their  early  youth,  and  to 
construct  many  interesting  devices  for  their 
protection.  Numerous  species,  shortly  after 
they  commence  to  shift  for  themselves? 
build  about  their  bodies  tubes  of  lime  (Fig. 
39),  from  which  they  may  emerge  to  gather 
food  and  into  which  they  may  dash  in  times 
of  danger.  As  the  worm  grows  the  tube  is 
correspondingly  enlarged,  and  these  tubes, 
in  all  stages  of  construction  and  variously 
coiled,  may  be  found  on  almost  every  avail- 
able  spot  at  the  seashore,  and  may  often 
be  seen  on  the  shells  of  oysters  in  the 
markets. 

In  other  species  the  tube  is  like  thin 
horn,  and  may  be  further  strengthened  or 
concealed  by  numerous  pebbles,  bits  of  carefully  selected 
seaweeds,  or  highly  tinted  shells,  which  give  them  a  very 
attractive  appearance.  Such  species  usually  develop  out 
of  immediate  contact  with  other  forms,  but  a  few  live 
so  closely  associated  together  that  their  twisted  tubes 


FIG.  38.— A  common 
marine  worm  (Po- 
lynas  brevisetosa), 
with  extended  pro- 
boscis  and  over- 
lapping plates  cov- 
ering the  back. 


62 


ANIMAL   FORMS 


form  great  stony  masses,  sometimes  several  feet  in  dia- 
meter. 

64.  Effects  of  an  inactive  life. — In  many  species  such  a 
sedentary  life  has  resulted  in  the  almost  complete  disap- 
pearance of  the  lateral  appendages,  which  therefore  no 
longer  serve  as  organs  of  respiration,  and  this  function  has 
been  shifted  accordingly  on  to  other  structures.  These 
new  organs  are  situated  principally  on  the  exposed  head, 


FIG.  39.— Sedentary  tube-dwelling  marine  worms,  upper  left  ha 

natural  size),  the  remainder  Serpula  (enlarged  twice).    From  life. 


(.one-half 


and  Fig.  39  shows  the  general  appearance  of  some  com- 
mon species.  The  corners  of  the  mouth  have  expanded 
into  great  plumes,  sometimes  wondrously  colored  like  a 
full-blown  flower,  and  these,  bounteously  supplied  with 
blood-vessels,  act  as  gills.  "When  disturbed,  the  plumes  are 
hastily  withdrawn  into  the  tube,  and  some  of  the  so-called 
serpulids  (Fig.  39,  bottom  of  figure)  close  the  entrance  with 
a  funnel-shaped  stopper.  While  the  plumes  are  primarily 
respiratory  organs,  they  also  act  as  delicate  feelers,  and  may 
even  bear  a  score  or  more  of  eyes ;  and  in  addition,  being 


THE  WORMS 


63 


Ph 


covered  with  cilia,  create  the  currents  of  water  which 
bring  minute  organisms  serving  as  food  within  reach  of 
the  mouth. 

65.  Development. — Unlike    the   earthworms,  the  Poly- 
chastes  lay  their  eggs  in  the  sea  water,  where  they  are  left 
alone  to  develop  as  best  they  may.     Both  the  male  and 
female  Nereis,  as  the  egg-laying  time  approaches,  undergo 
remarkable  changes  in  their  external  appearance,  resulting 
in  the  form   shown  in  Fig.   36,  A. 

They  are  now  active  swimmers,  and 
thus  are  able  to  scatter  the  fertilized 
eggs  over  wide  and  more  or  less  favor- 
able areas.  The  young  also  for  a 
time  are  free-swimming,  but  finally 
end  their  migrations  by  settling  to 
the  sea  bottom,  where  they  gradually 
attain  the  adult  condition. 

As  in  some  of  the  flatworms,  re- 
production may  also  arise  asexually 
by  the  division  of  the  animal  into  two 
or  more  parts,  each  of  which  subse- 
quently becomes  a  complete  indi- 
vidual. In  other  species  growth  of 
various  parts  may  result  in  two  com- 
plete worms  at  the  time  of  separation  ; 
and  from  such  forms  we  may  trace  a 
fairly  complete  series  up  to  those  in 
which  the  original  parent  breaks  up  FIG.  40.-A  leeci; 

.     .  la).    Right-hand  figure  il- 

into  twenty  to  thirty  young.  lustrau£  alimentary  canal. 

66.  The     leeches.  —  At     first     Sight        Ph,  pharynx  ;  c,  crop  ;  p, 

the  leeches  (Fig.  40),  or  at  least  the      latcral  pouche9;  '*"  in" 


smaller,  more  leaf-like  forms,  might 
be  mistaken  for  flatworms,  especially  for  some  of  the  para- 
sitic species.  As  in  the  latter,  the  mouth  is  surrounded  by 
a  sucker,  and  another  is  located  at  the  hinder  end  of  the 
body,  but  beyond  this  point  the  resemblance  ceases.  The 


64  ANIMAL  FORMS 

outer  surface  is  delicately  marked  off  into  eighty  or  a  hun- 
dred rings,  of  which  from  three  to  five  are  included  in  one 
of  the  deeper  true  segments  corresponding  to  those  of 
other  annelids.  From  two  to  ten  pairs  of  simple  eyes  are 
borne  on  the  head,  and  owing  to  the  fact  that  they  are 
active  swimmers,  or  move  by  caterpillar-like  looping,  loco- 
motor  spines  are  unnecessary  and  absent.  In  their  internal 
organization,  however,  there  are  many  features  which  in- 
dicate a  close  relationship  with  the  Oligochsetes  or  few- 
bristle  worms.  The  nervous,  circulatory,  and  certain  char- 
acteristics of  the  excretory  systems  are  decidedly  similar, 
but,  on  the  other  hand,  some  facts  are  difficult  to  explain 
on  such  a  theory,  and  have  led  some  zoologists  to  the  belief 
that  the  relationship  of  these  animals  can  not  at  present 
be  determined. 

67.  Haunts  and  habits.— The  leeches  usually  dwell  in 
among  the  plants  in  slowly  running  streams,  but  some 
occur  in  moist  haunts  on  land,  and  a  considerable  number 
live  in  the  sea.  All  are  "  bloodsuckers  " — fierce  carnivo- 
rous worms,  whose  bite  is  so  insidiously  made  that  the  vic- 
tim frequently  is  ignorant  of  their  presence.  Fishes,  frogs, 
and  turtles  are  the  most  frequently  attacked,  but  cattle  and 
other  animals  which  come  down  to  drink  also  become  their 
prey.  In  some  of  the  tropical  countries  the  land-leeches 
are  present  in  large  numbers  secreted  among  the  leaves,  and 
so  severe  are  their  attacks  that  various  animals,  even  man, 
succumb  to  their  united  efforts.  Adhering  by  their  suck- 
ers, they  puncture  the  skin,  some  using  triple  jaws,  and 
fill  themselves  until  they  become  greatly  distended,  when 
they  usually  drop  off  and  digest  the  meal  at  leisure.  In 
certain  species  the  intestine  is  provided  with  lateral 
pouches  (Fig.  40),  which  serve  to  store  up  the  food  until 
the  time  for  digestion  arrives.  A  full  meal  is  sufficient 
with  some  species  to  last  for  two  or  three  months,  and  the 
medicinal  or  horse-leech  when  gorged  with  food  may  con- 
sume a  year  in  digesting  it. 


THE  WORMS  65 

68.  Egg-laying. — The  eggs  of  some  leeches  are  stored 
up  in  a  cocoon  like  that  of  the  earthworm,  which  is  attached 
to  submerged  plants  or  placed  under  stones.  When  the 
young  are  able  to  lead  independent  lives  they  emerge  with 
the  form  of  the  parent.  A  leaf-like  form,  Clepsine,  some- 
times found  adhering  to  turtles,  fastens  the  eggs  to  the 
under  side  of  its  body,  and  the  young  when  hatched 
remain  there  for  several  days,  adhering  by  their  posterior 
suckers. 


CHAPTER  VII 


ANIMALS   OF   UNCERTAIN   RELATIONSHIPS 

IN  this  chapter  we  shall  consider  in  a  brief  way  a  number 
of  different  groups  of  animals  whose  relationships  are  un- 
certain. Up  to  the  present  time  the  study  of  their  habits, 
structure,  and  development  has  been  of  too  fragmentary 
or  unrelated  a  character  to  enable  the  majority  of  zoologists 
to  agree  upon  their  classification.  Nevertheless,  many  of 
them  are  highly  interesting  and  attractive, 
often  very  common,  and  in  some  respects 
they  hold  important  positions  in  the  animal 
kingdom. 

69.  The  rotifers  or  wheel-animalcules. — 
The  rotifers  or  wheel-animalcules  are  rela- 
tively small  and  beautiful  organisms,  rarely 
ever  longer  than  a  third  of  an  inch,  but  at 
times  so  abundant  that  they  may  impart  a 
reddish  tinge  to  the  water  of  the  streams 
and  ponds   in  which  they  live.     At  first 
sight  they  might  be  mistaken  for  one-celled 
animals,  but  the   presence   of  a  digestive 
tract  and  of  reproductive  elements  soon  dis- 
pels such  a  belief.   .Examined  under  the 
animaicuie"cffo«/7r).  microscope,  the  more   common   forms   are 
seen  to  possess  an  elongated  body  terminat- 
ing at  the  forward  end  in  two  disk-like  expansions  beset 
along  the  edges  with  powerful  cilia.     These  serve  to  drive 
the  animal  about,  or,  when  it  remains  temporarily  attached 


FIG.  41— A  whee 


ANIMALS  OF  UNCERTAIN   RELATIONSHIPS  6T 

by  the  sticky  secretion  of  the  foot,  to  sweep  the  food-par- 
ticles down  into  the  mouth.  Through  the  walls  of  the 
transparent  body  such  substances  are  seen  to  pass  into  the 
stomach,  where  they  are  rapidly  hammered  or  rasped  into 
a  pulp  by  the  action  of  several  teeth  located  there.  In 
the  absence  of  a  circulatory  system  the  absorbed  food  is 
conveyed  by  the  fluid  of  the  body-cavity,  which  also  con- 
veys the  wastes  to  the  delicate  kidneys.  Several  other 
features  of  their  organization  are  of  much  interest,  espe- 
cially to  the  zoologist,  who  believes  that  he  gains  from 
their  simple  structure  some  ideas  of  the  ancestors  of  the 
modern  worms,  mollusks,  and  their  allies.  During  the 
summer  the  rotifers  lay  two  sizes  of  "  summer  eggs," 
which  are  remarkable  for  developing  without  fertilization. 
The  large  size  give  rise  to  females,  the  smaller  to  males,  the 
latter  appearing  when  the  conditions  commence  to  be  un- 
favorable. The  "  winter  eggs,"  fertilized  by  the  males  and 
covered  with  a  firm  shell,  are  able  for  prolonged  periods  to 
Avithstand  freezing,  drought,  or  transportation  by  the  wind. 
The  adults  also  are  able  under  the  same  adverse  conditions 
to  surround  themselves  with  a  firm  protective  membrane 
and  to  exist  for  at  least  a  year.  Once  again  in  the  presence 
of  moisture  the  shell  dissolves,  and  in  a  surprisingly  short 
space  of  time  they  emerge,  apparently  none  the  worse  for 
the  prolonged  period  of  quiescence. 

70.  Gephyrea. — There  is  a  comparatively  large  group  of 
worm-like  organisms,  over  one  hundred  species  in  all,  which 
at  present  hold  a  rather  unsettled  position  in  the  animal 
kingdom.  Some  of  the  more  common  forms  (Fig.  42) 
living  in  the  cracks  of  rocks  or  buried  in  the  sand,  usually 
in  shallow  tide  pools  along  the  seashore,  have  a  spindle- 
shaped  body  terminated  at  one  end  by  a  circlet  of  tentacles 
which  surround  the  mouth.  On  account  of  their  external 
resemblance  to  many  of  the  sea-cucumbers  (Fig.  92),  they 
were  earlier  associated  in  the  same  group ;  but  an  examina- 
tion of  their  internal  organization  inclines  many  zoologists 


68 


ANIMAL   FORMS 


to  the  belief  that  the  ancestors  of  some  of  these  animals 
were  segmented  worms  whose  present  condition  has  arisen 
possibly  in  accordance  with  their  sluggish  habits.  This 
view  is  strengthened  by  the  fact  that  in  a  very  few  species 

the-  larvae  are  dis- 
tinctly segmented, 
but  lose  this  char- 
acter in  becoming 
adult.  As  before 
mentioned,  the 
greater  number  of 
species  live  in  bur- 
rows in  the  sand 
or  crevices  in  the 
rocks,  from  which 
they  reach  out  and 
gather  in  large 
^quantities  of  sand. 
As  these  substances 

FIG.  42.— Agephyrean  worm  (Dendrostoma).    Specimen    pass    down    the    in- 
on  left  opened  to  show  k,  kidney,  m,  muscle  bands,     ,       , .  ,, 

and «.«.,  nerve-cord.  testme     the     niltri- 

tive  matters  are  di- 
gested and  absorbed,  while  the  indigestible  matters  are 
voided  to  the  exterior.  When  large  numbers  are  associated 
together  they  are  doubtless  important  agents  in  modifying 
the  character  of  the  sea  bottom,  thus  acting  like  the  earth- 
worms and  their  relatives. 

71.  The  sea-mats  (Polyzoa). — The  sea-mats  or  Polyzoa 
constitute  a  very  extensive  group  of  animals  common  on 
the  rocks  and  plants  along  the  seashore,  and  frequently 
seen  in  similar  situations  in  fresh-water  streams.  A  few 
lead  lives  as  solitary  individuals,  but  in  the  greater  number 
of  species  the  original  single  animal  branches  many  times, 
giving  rise  to  extensive  colonies.  In  some  species  these 
extend  as  low  encrusting  sheets  over  the  objects  on  which 
they  rest;  while  in  others  the  branches  extend  into  the 


AXIMALS  OF  UXCERTAIX    RELATIOXSHIPS  60 

surrounding  medium  and  assume  feathery  shapes  (Fig.  43), 
which  often  bear  so  close  a  resemblance  to  certain  plants 


FIG.  43.-Lamp-shells 


eft  of  figure),  fossil  and  living,  and  (.on 


right)  plant-like  colonies  of  sea-mats. 


that  they  are  frequently  preserved  as  such.  What  their 
exact  position  is  in  the  animal  scale  it  is  somewhat  difficult 
to  say ;  but  judging  especially  from  their  development,  it 
appears  probable  that  they  are  distant  relatives  of  the  seg- 
mented worms. 


70  ANIMAL  FORMS 

72.  Lamp-shells  or  Brachiopods. — Occasionally  one  may 
find  cast  on   the  beach  or   entangled   in   the    fishermen's 
lines  or  nets  a  curious  bivalve  animal  similar  to  the  form 
shown  in  Fig.  43.      These  are  the  Brachiopods,  or  lamp- 
shells.     The  remains  of  closely  related  forms   are   often 
abundant  as  fossils  in  the  rocks  (Fig.  43).    Over  a  thousand 
species  have  been  preserved  in  this  way,  and  we  know  that 
in  ages  past  they  nourished  in  almost  incredible  numbers 
and  were  scattered  widely  over  the  earth.    Unable  to  adapt 
themselves  to  changing  conditions  or  unable  to  cope  with 
their  enemies,  they  have  gradually  become  extinct,  until 
to-day  scarcely  more  than  one  hundred  species  are  known. 
These  are  often  of  local  distribution,  and  many  are  com- 
paratively rare. 

For  a  long  period  the  Brachiopods,  owing  to  their  pecul- 
iar shells,  were  classed  together  with  the  clams  and  other 
bivalve  mollusks.  The  presence  of  a  mantle  also  strength- 
ened the  belief ;  but  closer  examination  during  more  recent 
years  has  shown  that  the  shells  are  dorsal  and  ventral,  and 
not  arranged  against  the  sides  of  the  animal  as  in  the 
clams.  Another  peculiar  structure  consists  of  two  great 
spirally  coiled  "  arms,"  which  are  comparable  in  a  general 
way  to  greatly  expanded  lips.  The  cilia  on  these  create,  in 
the  water  currents  which  sweep  into  the  mouth,  the  small 
animals  and  plants  that  serve  as  food.  The  internal  organ- 
ization resembles  in  a  broad  way  that  of  the  animals  con- 
sidered in  the  previous  section,  and  it  now  appears  that 
both  trace  their  ancestry  back  to  the  early  segmented 
worms. 

73.  Band  or  nemertean  worms. — In  a  few  cases  band  or 
nemertean  worms  have  been  discovered  in  damp  soil  or  in 
fresh-water  streams.    These  are  commonly  small  and  incon- 
spicuous, and  are  pigmies  when  compared  with  their  marine 
relatives,  which  sometimes  reach  a  length  of  from  fifty  to 
eighty  feet.     Many  of  the  marine  species  (Fig.  44)  are  often 
found  on  the  seashore  under  rocks  that  have  been  exposed 


ANIMALS  OF  UNCERTAIN  RELATIONSHIPS 


71 


B 


by  the  retreating  tide.  They  are  usually  highly  colored 
with  yellow,  green,  violet,  or  various  shades  of  red,  and  are 
so  twisted  into  tangled 
masses  that  the  differ- 
ent parts  of  the  body 
are  indistinguishable. 
As  the  animal  crawls 
about,  a  long  thread- 
like appendage,  the  pro- 
boscis, is  frequently  shot 
out  from  its  sheath  at 
the  forward  end  of  the 
body  and  appears  to  be 
used  as  a  blind  man 

USeS  his  Stick.      At  Other    FIG.  44.-A  band  or  nemertean  worm.    A,  entire 
worm  ;  B,  head,  bearing  numerous  eyes  and 
times,  when  Small  WOrmS  spine-tipped  proboscis. 

and  other  animals  are 

encountered,  the  proboscis  is  shot  out  farther  and  with 
greater  force,  impaling  the  victim  on  a  sharp  terminal  spine 
(Fig.  44).  The  food  is  now  borne  to  the  mouth,  located 
near  the  base  of  the  proboscis,  is  passed  into  the  digestive 
tract,  traversing  the  entire  length  of  the  body,  and  is  far- 
ther operated  on  by  systems  of  organs  too  complex  to  be 
considered  here. 


CHAPTEK  VIII 

MOLLUSKS 

74.  General  characters. — For  very  many  years  the  mol- 
lusks — that  is,  the  clams,  snails,  cuttlefishes,  and  their  allies 
— have  been  favorite  objects  of  study  largely  because  of  the 
durability,  grace,  and  coloration  of  the  shell.     The  latter 
may  be  univalve,  consisting  of  one  piece,  as  in  the  snails,  or 
bivalve,  as  in  the  clams  and  mussels,  and  may  possess  almost 
every  conceivable  shape,  and  vary  in  size  from  a  grain  of 
rice  to  those  of  the  giant  clam  (Tridacna)  of  the  East  Indian 
seas,  which  sometimes  weighs  five  hundred  pounds.    These 
external  differences  are  but  the  expression  of  many  internal 
modifications,  which,  while  adapting  these  animals  for  dif- 
ferent modes  of  life,  are  yet  not  sufficient  to  disguise  a 
more  fundamental  resemblance  which  exists   throughout 
the  group.     In  some  respects  the  mollusks  show  a  close 
resemblance  to  the  annelid  worms,  but,  on  the  other  hand, 
the  body  is  usually  more  thick-set  and  totally  devoid  of  any 
signs  of  segmentation.     In  every  case  the  skin  is  soft  and 
slimy,  demanding  moist  haunts  and  usually  the  protection 
of  a  shell,  and  the  body  is  modified  along  one  surface  to 
form  a  foot  or  creeping  disk  which  serves  in  locomotion. 
The  internal  organization  is  somewhat  uniform,  and  will 
admit   of  a   general   description   later   on.     Mollusks   are 
divided  into  three  classes,  viz. :  The  Lamellibranchs,  em- 
bracing the  clams  ;   the  Gasteropods,  or  snails ;  and  the 
Cephalopods,  or  cuttlefishes,  squids,  and  related  forms. 

75.  Lamellibranchs  (clams  and  mussels). — Numerous  rep- 
resentatives of  this  class,  such  as  the  clams  and  mussels, 

72 


MOLLUSKS  T3 

occur  along  our  seacoasts  or  are  plentifully  distributed  in 
the  fresh-water  streams  and  lakes.  They  are  distinguished 
from  other  mollusks  by  a  greatly  compressed  body,  which 
is  enclosed  in  a  shell  consisting  of  two  pieces  or  valves 
locked  together  by  a  hinge  along  the  dorsal  surface.  Rais- 
ing one  of  these  valves,  the  main  part  of  the  body  may  be 
seen  to  occupy  almost  completely  the  upper  (dorsal)  part 
of  the  shell  (Fig.  45),  and  to  be  continued  below  into  the 
muscular  hatchet-shaped  foot  (ft.},  which  aids  the  clam  in 
plowing  its  way  through  the  sand  or  mud  in  which  it  lives. 
Arising  on  each  side  of  the  back  of  the  animal  and  extend- 
ing its  entire  length  is  a  great  fold  of  skin,  which  com- 
pletely lines  the  inner  surface  of  the  corresponding  valve 
of  the  shell.  These  are  the  two  mantle  lobes  (m)  instru- 
mental in  the  formation  of  the  shell,  and  enclosing  between 
them  a  space  containing  the  foot  and  a  number  of  other 
important  structures,  the  most  conspicuous  of  which  are 
the  gills  (g),  consisting  of  two  broad,  thin  plates  attached 
along  the  sides  of  the  animal  and  hanging  freely  into  the 
space  (mantle  cavity)  between  the  mantle  and  the  foot. 
Owing  to  this  lamella-like  character  of  the  branchia  or  gills 
the  class  derives  its  name,  lamellibranch.  To  illustrate  the 
relations  of  these  various  organs  to  one  another  the  clam  has 
been  compared  to  a  book,  in  which  the  shells  are  repre- 
sented by  the  cover,  the  fly-leaves  by  the  mantle  lobes,  the 
first  two  and  last  two  pages  by  the  gills,  and  the  remaining 
leaves  by  the  foot.  In  the  clams,  however,  the  halves  of 
the  mantle,  like  the  halves  of  the  shell,  are  curved,  and 
thus  enclose  a  space,  the  mantle  cavity,  which  is  partly 
filled  by  the  gills  and  foot. 

Unlike  the  other  mollusks  which  usually  lead  active 
and  more  aggressive  lives,  the  clams  show  scarcely  a  sign  of 
a  head  and  tentacles,  and  other  sense  organs  are  likewise 
absent  from  this  region.  The  mouth  also  lacks  definite 
organs  of  mastication,  and  as  devices  for  catching  and 
holding  food  are  not  developed,  the  food  is  brought  to  the 


T4  ANIMAL  FORMS 

mouth  by  means  of  the  cilia  on  the  great  triangular  lipa  or 
palps  which  bound  it  on  each  side  (Fig.  45,  A,j9). 


FIG.  45.— Anatomy  of  fresh-water  clam.  A,  right  valve  of  shell  removed  ;  B,  dissec 
tion  to  show  internal  organs,  a,  external  opening  of  kidney ;  a.a.,  the  anteYior 
muscle  for  closing  the  shell ;  b,  opening  of  reproductive  kidney  ;  c.  brain  ;  //., 
foot ;  g,  gill ;  h,  heart ;  i,  intestine  ;  k,  kidney  ;  I,  liver  ;  m,  mantle  (upper  fig.), 
mouth  (lower  fig.) ;  p,  palp  (upper  fig.),  foot  nerves  (lower  fig.) ;  p.a.,  hinder 
muscle  for  closing  the  shell  ;  #.  space  through  which  the  water  passes  on 
leaving  the  body  ;  si,  stomach  ;  v,  nerves  snpplying'viscera. 

Between  the  halves  of  the  shell  in  the  hinge  region  is  a 
horny  pad  that  acts  like  a  spring,  and  without  any  muscu- 
lar effort  on  the  part  of  the  clam  keeps  the  shells  open. 


MOLLUSKS  75 

These  are  also  united  by  two  great  adductor  muscles,  located 
at  opposite  ends  of  the  animal  (Fig.  45,  A,  a.a.,  J9.a.),  which 
in  times  of  disturbance  contract  and  firmly  close  the  shell. 
Upon  their  relaxation  the  shell  opens,  the  clam  extends  its 
foot,  and  plows  its  way  leisurely  through  the  mud,  or  re- 
mains buried,  leaving  only  the  hinder  portion  of  its  gaping 
shell  exposed.  Through  this  opening  a  current  of  water 
is  continually  passing  in  and  out,  owing  to  the  action  of 
the  cilia  covering  the  gills,  and  by  placing  a  little  car- 
mine or  coloring  matter  in  the  ingoing  stream  we  may 
trace  its  course  through  the  body.  Passing  in  between  the 
mantle  and  the  foot  it  travels  on  toward  the  head,  giving 
off  small  side  streams  which  are  continually  made  to  enter 
minute  openings  in  the  gills,  whence  they  are  conducted 
through  tubes  in  each  gill  up  to  a  large  canal  at  its  base, 
where  it  is  carried  backward  to  the  exterior.  In  this  pro- 
cess oxygen  gas  is  supplied  to  the  number  of  blood-ves- 
sels traversing  the  gills,  and  at  the  same  time  considerable 
quantities  of  minute  organisms  and  organic  debris  are 
hurried  forward  toward  the  head,  where  they  encounter  the 
whirlpools  made  by  the  cilia  on  the  lips  and  are  rapidly 
whisked  down  into  the  mouth  and  swallowed. 

75.  Rock-  and  wood-boring  clams. — Other  similar  forms 
are  rendered  even  more  secure  through  their  ability  to 
bore  in  solid  rock.  In  the  common  Piddock,  for  example 
(Fig.  46),  the  shell  is  beset  with  teeth  like  a  rasp,  which 
gradually  enlarge  the  cavity  as  the  animal  grows,  until  it 
becomes  a  prisoner  with  no  means  of  communication  with 
the  exterior  save  the  small  opening  through  which  the 
siphons  project.  This  is  also  the  case  with  the  Teredo, 
improperly  called  the  shipworm,  which  swims  about  for 
some  time  during  early  life  and  then,  about  the  size  of  a 
small  pinhead,  settles  down  upon  the  timbers  of  wharves 
or  unsheathed  ships,  into  which  it  rapidly  tunnels. 
Throughout  life  its  excavation  is  extended  sometimes  to  a 
distance  of  two  to  three  feet,  and  imprisoned  yet  safe  at 


76 


ANIMAL   FORMS 


the  bottom  of  its  burrow,  it  extends  its  slender  siphons  up 
the  tube  and  out  of  the  entrance  for  its  food  supply. 
Often  hundreds  of  individuals  enter  the  same  piece  of 
wood,  which  becomes  thoroughly  riddled  within  a  short 


FIG.  46.— The  piddock  (Zirph&a 


time,  and  though  giving  no  outward  sign  of  weakness  may 
collapse  with  its  own  weight.  Incalculable  damage  is  thus 
rendered  to  the  shipping  interests,  and  in  consequence 
much  has  been  done  to  check  their  ravages,  but  they  are 
far  from  being  completely  overcome. 

76.  Other  stationary  species. — A  large  number  of  other 
species,  while  small  and  inconspicuous,  are  also  free  to 


MOLLUSKS 


77 


move  about,  but  as  they  become  larger  they  lose  this  ability 
either  wholly  or  periodically.  In  the  edible  mussels  (Myti- 
lus,  Fig.  47),  for  example,  which  are  associated  in  great 
numbers  on  the  rocks  along  our  coasts,  the  foot  early  be- 
comes long  and  slender  and  capable  of  reaching  out  a  con- 
siderable distance  from  the  shell  to  attach  threads  (byssus), 
which  it  spins,  to  foreign  objects.  These  are  remarkably 
strong,  and  when  several  have  been  spun  it  becomes  a  mat- 
ter of  much  difficulty  to  dislodge  them.  After  remaining 
anchored  in  one  situation  for  a  while  the  mussel  may  vol- 


FIG.  47. — The  edible  mussel  (Mytilus  edulin),  showing  the  threads  by  which  it  is 
attached.    Natural  size,  from  life. 

untarily  free  itself,  and  in  a  labored  fashion  move  to  some 
other  more  favorable  spot  where  it  again  becomes  attached, 
but  there  are  numerous  species,  such  as  "fan  shells" 
(Pinna),  scallops,  Anomia,  and  a  few  fresh-water  forms, 
where  the  union  is  permanent. 

Finally,  in  the  oysters,  some  of  the  scallops,  and  a  num- 
ber of  less  familiar  forms,  the  young  in  very  early  life  drop 
down  upon  some  foreign  object  to  which  the  shell  soon 
becomes  firmly  attached,  and  in  this  same  spot  they  pass 
the  remainder  of  their  lives.  The  oyster  usually  falls  upon 
the  left  half  of  its  shell,  which  becomes  deep  and  capacious 
enough  to  contain  the  body,  while  the  smaller  right  valve 


78  ANIMAL  FORMS 

acts  as  a  lid.  As  locomotion  is  out  of  the  question,  the  foot 
never  develops,  and  the  shell  is  held  by  only  one  adductor 
muscle,  whose  point  of  attachment  in  the  oyster  is  indicated 
by  a  brown  scar  in  the  interior  of  the  shell. 

77.  Internal  organization. — It  is  thus  seen  that  the  ex- 
ternal features  of  the  clam  are  variously  modified,  according 
to  the  life  of  the  animal,  but  the  internal  organization  is 
much  more  uniform.  In  nearly  every  species  the  food  con- 
sists of  floating  organisms,  which  are  driven  by  the  palps 
into  the  mouth  and  on  to  the  simple  stomach,  where  it  is 
subjected  to  the  solvent  action  of  the  fluids  from  the  liver 
(Fig.  45,  B,  /)  before  entering  the  intestine.  This  latter 
structure  is  usually  of  considerable  length,  and  in  the  active 
species  extends  down  into  the  foot,  and  it  is  also  peculiar  in 
penetrating  the  ventricle  of  the  heart.  Traversing  the  in- 
testine the  nutritive  portion  of  the  food  is  absorbed,  and  is 
conveyed  over  the  body  by  a  circulatory  system  more  highly 
developed  than  in  the  higher  worms.  On  the  dorsal  side 
of  the  clam,  in  a  spacious  pericardial  chamber,  the  large 
heart  is  situated  (Fig.  45,  h),  consisting  of  a  median  highly 
muscular  ventricle  surrounding  the  intestine  and  of  two 
thin  auricles,  one  on  either  side.  From  the  former,  two 
arteries  with  their  numerous  branches  convey  the  blood  to 
all  parts  of  the  body,  where  it  accumulates,  not  in  capilla- 
ries and  veins,  but  in  spaces  or  sinuses  among  the  muscles 
and  various  organs,  constituting  a  somewhat  indefinite  sys- 
tem of  channels  which  lead  to  the  gills  and  kidneys.  In 
these  latter  organs  the  blood  delivers  up  the  waste  which  it 
has  accumulated  on  its  journey,  and  absorbing  a  supply  of 
oxygen,  it  flows  into  the  great  auricles,  which  in  turn  pass 
it  into  the  ventricle  to  circulate  once  more  throughout 
the  body. 

The  excretory  apparatus,  consisting  usually  of  two  kid- 
neys, of  which  one  may  degenerate  in  many  snails,  bears  a 
close  resemblance  to  that  of  the  annelids.  In  the  clam,  for 
instance,  each  consists  of  a  bent  tube  symmetrically  ar- 


MOLLUSKS  79 

ranged  on  each  side  of  the  body  (Fig.  45,  B,  &),  and  the  inner 
ends  («),  corresponding  to  the  ciliated  funnel  of  the  anne- 
lid kidney,  open  into  the  pericardial  cavity.  Their  walls 
are  continually  active  in  extracting  wastes  from  the  blood 
supplied  to  them,  and  these,  together  with  the  substances 
swept  out  from  the  pericardial  cavity,  traverse  the  tube  and 
are  carried  to  the  exterior.  In  other  mollusks  the  kidney 
may  be  more  compact,  or  greatly  elongated,  or  otherwise 
peculiar,  but  in  reality  they  bear  a  close  resemblance  to 
those  of  the  clam. 

78.  Nervous  system. — The  nervous  system,  like  the  ex- 
cretory, differs  considerably  in  different  mollusks,  yet  the 
resemblances  are  fairly  close  throughout.     In  the  clam  the 
cerebral  ganglia  corresponding  to  the  "  brain  "  in  annelids 
is  located  at  either  side,  or  above  the  mouth,  and  from  it 
several  nerves  arise,  the  larger  passing  downward  to  two 
pedal  ganglia  ( p)  embedded  in  the  foot  and  to  the  visceral 
ganglia  (v)  far  back  in  the  body  (Fig.  45,  B).     These  nerve 
centers  continually  send  out  impulses  which  regulate  the 
various  activities  of  the  body  and  also  receive  impressions 
from  without.     These  come  chiefly  through  the  sense  of 
touch,  for  in  the  clams  the  other  senses  are  usually  either 
feebly  developed  or  altogether  absent. 

79.  Development.— In  the  mollusca  new  individuals  al- 
ways arise  from  eggs,  which  are  commonly  deposited  in  the 
water  and  there  undergo  development.     In  the  fresh-water 
clams  the  reproductive  organ  is  usually  situated  in  the  foot 
(Fig.  45),  while  in  the  oyster  and  similar  inactive  species  it  is 
attached  to,  the  large  adductor  muscle.    In  these  latter,  and 
in  many  other  marine  forms,  the  eggs  are  shed  directly  into 
the  sea,  where  they  are  left  to  undergo  their  development 
buffeted  by  winds  and  waves  and  subject  to  the  attack  of 
numerous  enemies.     Under  such  circumstances  the  chances 
of  survival  are  slight,  and  for  this  reason  eggs  are  laid  in 
vast  numbers,  which  have  been  variously  estimated  for  the 
oyster,  for  example,  from  two  to  forty  million.     Develop- 


80  ANIMAL  FORMS 

ment  proceeds  at  first  much  as  in  the  sponge,  but  soon  the 
shell,  foot,  gills,  and  various  other  molluscan  structures 
put  in  an  appearance,  and  the  few  surviving  young  Avhich 
have  been  free-swimming  now  settle  down  in  some  favor- 
able spot,  and  attach  themselves  or  burrow  according  to 
their  habit. 

80.  Life  history  of  fresh-water  clams. — The  life  history  of 
our  common  fresh-water  clams  is  perhaps  one  of  the  most 
remarkable  known  among  mollusks.     The  parent  stores  the 
eggs,  as  soon  as  they  are  laid,  in  the  outer  gill  plate,  and 
there,  well  protected,  they  undergo  the  first  stages  of  their 
development,  which  results  in  the  formation  of  minute 
young  enclosed  in  a  bivalve  shell  beset  with  teeth.     These 
are  often  readily  obtained,  sometimes  as  they  are  escaping 
from  the  parent,  and  when  examined  under  the  microscope 
are  seen  to  rapidly  open  and  close  their  shells  in  a  snapping 
fashion  when  in  the  least  disturbed.     In  a  state  of  nature 
this  latter  movement  may  result  in  attaching  the  young  to 
the  fins  or  gills  of  some  passing  fish,  which  is  necessary  to 
its  further  development.     Within  a  short  time  it  becomes 
completely  embedded  in  the  flesh  of  its  host,  from  which, 
as  a  parasite,  it  draws  its  nourishment,  and  during  the 
next  few  weeks  undergoes  a  wonderful  series  of  transforma- 
tions resulting  in  a  small  mussel,  which  breaks  its  way 
through  the  thin  skin  of  the  fish  and  drops  to  the  bottom. 

81.  The  gasteropods. — The  gasteropods,  including  snails, 
slugs,  limpets,  and  a  host  of  related  forms,  fully  twenty 
thousand  different  species  in  all,  are  found  in  most  of  our 
fresh-water  streams  and  lakes  and  in  moist  situations  on 
land,  while  great  numbers  live  along  the  seashore  and  at 
various  depths  in  the  ocean,  even  down  as  far  as  three 
miles.     Examining  any  of  them  carefully  we  find  many  of 
the  same  organs  as  in  the  clams,  but  curiously  changed  and 
adapted  for  a  very  different  and  usually  active  life.     In  our 
common  land  snails  (Fig.  48),  which  we  may  well  examine 
before  passing  on  to  a  general  survey  of  the  group,  the  first 


MOLLUSKS  81 

striking  peculiarity  is  in  the  univalve  shell,  with  numerous 
whorls,  into  which  the  animal  may  at  any  time  withdraw 
completely.  Ordinarily  this  is  carried  on  the  back  of  the 
spindle-shaped  body,  which  is  fashioned  beneath  into  a  great 


Fio.  48.— The  slug  (Ariolimax)  and  commoi 


flat  sole  or  creeping  surface  that  bears  on  its  forward  bor- 
der a  wide  opening  through  which  mucus  is  continually 
issuing  to  enable  the  snail  to  slip  along  more  readily.  Slime 
also  exudes  on  other  points  on  the  surface  of  the  body  and 
affords  a  valuable  protection  against  excessive  heat  and 
drought. 

Unlike  the  clams,  the  forward  end  of  the  body  is  devel- 
oped into  a  well-marked  head  bearing  the  mouth  and  a 
complicated  mechanism  for  gathering  and  masticating  food, 
together  with  two  pairs  of  tentacles,  one  of  which  carries  the 
eyes.  On  the  right  side  of  the  animal,  some  distance  behind 
the  head,  is  the  opening  of  the  little  sac-like  mantle  cavity 
(Fig.  48)  which  contains  the  respiratory  organs,  and  into 
which  the  alimentary  canal  and  the  kidneys  pour  their 
wastes.  The  relation  of  these  organs  to  the  mantle  cavity 
is  the  same  as  in  the  clams,  though  the  cavities  differ  much 
in  size  and  position. 

82.  Other  snails.  The  shell.— Extending  our  acquaint- 
ance to  other  species  of  snails,  we  find  the  same  general 
plan  of  body,  although  somewhat  obscured  at  times  by 


82  ANIMAL  FORMS 

many  modifications.  A  foot  is  generally  present,  also  a 
more  or  less  well-developed  head,  and  the  body  is  usually 
surrounded  by  a  shell  which  varies  widely  in  shape  and 
size  in  different  species.  In  the  common  limpets  the  early 
coiled  shell  is  transformed  into  an  uncoiled  cap-like  one, 
and  in  the  keyhole  limpets  is  perforated  at  its  summit.  The 

chitons  or  armadillo- 
snails  (Fig.  49),  often 
found  associated  with 
the  limpets,  carry  a 
most  peculiar  shell  con- 
sisting of  eight  plates, 
which  enables  the  ani- 
mal to  roll  up  like  an 
armadillo  when  dis- 

FIG.  49. -The  chiton,  armadillo-snail  or  sea-era-  tlirbed.        A    shell    is    by 
die.     The  left-hand  figure  shows  mouth  in  ., 

center  of  proboscis,  the  broad  foot  on  each  no     means    a    necessity, 

side  of  which  are  numerous  small  gills.  The  however,    f Or     in     many 
right-hand  figure  shows  the  mantle  and  shell,  , 

composed  of  eighties.     From  life,  one-  Species,      Such      as      the 

half  natural  size.  beautiful  naked  snails 

or  Xudibranchs  (Fig. 

50)  common  along  our  coasts,  it  may  be  entirely  absent, 
or,  as  in  the  ordinary  slugs,  reduced  to  a  small  scale  em- 
bedded in  the  skin. 

83.  Respiration. — A  considerable  quantity  of  oxygen  is 
absorbed  through  the  skin,  as  in  all  mollusks,  but  the  chief 
part  of  the  process  is  usually  taken  by  the  plume-like  gills, 
one  or  two  in  number,  which  are  located  in  the  mantle 
cavity.  In  the  chitons  (Fig.  49)  the  number  of  gills  is 
greater,  amounting  in  some  species  to  over  a  hundred, 
while  in  the  Xudibranchs  (Fig.  50)  gills  are  absent,  their 
places  being  taken  by  more  or  less  feathery  expansions  of 
the  skin  on  the  dorsal  surface. 

Many  of  the  gasteropods  left  exposed  on  the  rocks  by  a 
retreating  tide  retain  water  in  the  mantle  cavity,  from 
which  they  extract  the  oxygen  until  submerged  again. 


MOLLUSKS  83 

Others  breathe  by  means  of  gills  while  under  water,  and  by 
the  surface  of  the  body  and  the  moist  walls  of  the  mantle 


FIG.  50.— Three  different  species  of  naked  marine  snails  or  Nudibranchs.    Natural 
size,  from  life. 

cavity  when  exposed.  In  some  of  the  small  Littorinas 
attached  so  far  from  the  sea  as  to  be  only  occasionally 
washed  by  the  surf  this  latter  method  may  prevail  for  days 
together — in  fact  they  live  better  out  of  water  than  in  it. 
It  is  not  difficult  to  imagine  that  such  forms,  keeping  in 
moist  places,  might  wander  far  from  the  sea,  and,  losing 
their  gills,  become  adapted  to  a  terrestrial  life.  It  is 
believed  that  in  past  times  this  has  actually  occurred,  and 
that  our  land  forms  trace  their  descent  from  aquatic  ances- 
tors. To-day  they  breathe  by  a  lung — that  is,  they  take 
oxygen  through  the  walls  of  the  mantle  cavity,  as  the  slug 
may  be  seen  to  do,  though  in  some  species  traces  of  the  old 
gill  yet  remain. 

84.  Food  and  digestive  system. — Many  mollusks  live  upon 
seaweeds,  and  the  greater  number  of  terrestrial  forms  are 
fond  of  garden  vegetables  or  certain  kinds  of  lichens,  but, 
on  the  other  hand,  the  latter,  together  with  a  large  number 
of  marine  snails,  are  carnivorous.  In  all  cases  the  food 
requires  to  be  masticated,  and,  unlike  the  clams,  the  mouth 
is  usually  provided  with  horny  jaws,  and  an  additional 


ANIMAL  FORMS 


FIG.  51.— A  small  portion  of  the  radnla  or 
tongue-rasp  of  a  snail  (Sycolypus). 


masticatory  apparatus  which  consists  of  a  kind  of  tongue 
with  eight  to  forty  thousand  minute  teeth  in  our  land 
forms  (Fig.  51),  while  in  certain  marine  snails  they  are 
beyond  computation.  With  the  licking  motion  of  the 
tongue  this  rasp  tears  the  food  into  shreds  before  it  is 
swallowed,  and  in  the  whelks  or  borers  it  serves  to  wear  a 
circular  hole  through  the  shells  of  other  mollusks,  which 
are  thus  killed  and  devoured. 
This  latter  process,  is  facili- 
tated by  the  secretion  of  the 
salivary  glands,  which  has  a 
softening  effect  upon  the 
shell.  Ordinarily  the  saliva 
of  snails  exercises  some  di- 
gestive action. 

In  the  stomach  of  some 
snails  are  teeth  or  horny 
ridges  which  also  are  instrumental  in  crushing  the  food, 
and  in  numerous  minor  respects  peculiarities  exist  in  differ- 
ent species  according  to  the  nature  of  the  food;  but  in  its 
general  features  the  digestive  tract  is  similar  to  that  of 
the  clams. 

The  processes  of  circulation  and  excretion  are  also  car- 
ried on  by  means  of  systems  which  show  a  certain  resem- 
blance to  those  of  the  clams.  As  might  be  expected,  certain 
differences  exist,  sometimes  very  great,  but  they  are  of  too 
technical  a  nature  to  concern  us  further. 

85.  Sense-organs  of  lamellibranchs  and  gasterqpods. — 
The  eyes  of  mollusks  differ  widely  in  their  structure  and 
the  position  they  occupy  in  the  body.  In  our  common 
land  snails  two  pairs  of  tentacles  are  borne  on  the  head, 
the  lower  acting  as  feelers,  while  each  of  the  upper  ones 
bears  on  its  extremity  the  eye,  appearing  as  a  minute  black 
dot  (Fig.  48).  In  this  same  position  the  eyes  of  many 
marine  snails  occur,  but  there  are  numerous  species  in 
which  there  are  other  accessory  eyes.  In  many  of  the 


MOLLUSKS  85 

limpets,  for  instance,  there  are  numbers  of  additional  eyes 
carried  on  the  mantle  edge  just  under  the  eaves  of  the 
shell,  and  forming  a  row  completely  encircling  the  body. 
(In  the  scallops  there  are  two  rows  of  brilliantly  colored 
eyes,  set  like  jewels  on  the  edges  of  the  mantle  just  within 
the  halves  of  the  shell.)  In  the  chitons  the  eyes  of  the 
head  disappear  by  the  time  the  animal  attains  maturity, 
and  in  some  species  at  least  their  place  appears  to  be  taken 
by  great  numbers  of  eyes,  sometimes  thousands,  which  are 
embedded'  in  the  shells.  On  the  other  hand,  eyes  are  com- 
pletely absent  in  certain  species  of  burrowing  snails  and  in 
several  living  in  the  gloomy  depths  of  the  sea  far  from  the 
surface  ;  they  appear  to  be  absent  also  from  fresh-water 
clams ;  but  the  fact  that  certain  species  close  their  shell 
when  a  shadow  falls  upon  them,  leads  to  the  belief  that 
while  actual  eyes  are  not  present  the  skin  is  extremely 
sensitive  to  light.  This  is  also  the  case  with  many  snails. 
'  86.  Smell. — Since  the  sense  of  sight  is  generally  unde- 
veloped in  the  mollusks,  they  rely  chiefly  upon  touch  and 
smell  for  recognizing  the  presence  of  enemies  and  food. 
Tentacles  upon  the  head  and  other  parts  of  the  body,  and 
a  skin  abundantly  supplied  with  nerves,  show  them  to  pos- 
sess a  high  degree  of  sensibility ;  but  in  the  greater  num- 
ber of  species  the  sense  of  smell  is  of  chief  importance. 
Many  experiments  show  that  tainted  meat  and  strongly 
scented  vegetables  concealed  from  sight  and  several  feet 
distant  from  many  of  our  land  and  sea  mollusks  will  attract 
them  at  once.  In  these  forms  the  sense  of  smell  appears  to 
be  located  on  the  tentacles,  but  additional  organs,  possibly 
of  smell,  are  located  on  various  portions  of  the  body,  usu- 
ally in  the  neighborhood  of  the  gills. 

87.  Taste  and  hearing. — Several  mollusks  appear  to  be 
almost  omnivorous,  but  others  are  decidedly  particular  in 
their  choice  of  food,  which  leads  us  to  suspect  that  they 
possess  to  some  extent  the  sense  of  taste.  Nerves  supply- 
ing the  base  of  the  mouth  have  also  been  detected,  which 


86  ANIMAL  FORMS 

may  be  those  of  taste ;  but  experiments  along  the  line  are 
difficult  to  perform,  and  our  knowledge  of  this  subject  is 
far  from  complete.  The  same  is  true  of  hearing.  Certain 
organs,  interpreted  as  ears  and  located  in  the  foot,  have 
the  form  of  two  hollow  sacs,  containing  one  or  more  solid 
particles  of  sand  or  lime,  whose  jarrings,  when  effected  by 
sonorous  bodies,  may  result  in  hearing.  On  the  other  hand, 
it  is  held  by  some  that  they,  like  the  semicircular  canals  of 
higher  animals,  may  regulate  the  muscular  movements 
which  enable  the  animal  to  keep  its  balance. 

88.  Egg-laying  habits  and  development.— The  egg-laying 
habits  of  the  gasteropods  differ  almost  as  widely  as  their 
haunts.     The  terrestrial  forms  lay  comparatively  fevr  eggs, 
ranging  in  size  from  small  shot  to  a  pigeon's  egg  in  some 
of  the  tropical  species.     These  are  buried  in  hollows  in  the 
ground  or  under  sticks  and  stones,  and  after  a  few  weeks 
hatch  out  young  snails  having  the  form  of  the  adult.    The 
same  is  also  true  of  most  of  the  fresh-water  snails,  which 
lay  relatively  smaller  eggs  embedded  in  a  gelatinous  mass 
frequently  found  attached  to  sticks  and  leaves,  or  on  the 
walls  of  aquaria  in  which  they  are  confined.     Many  marine 
species   construct  capsules   of  the  most   varied  patterns 
which  they  attach  to  different  objects,  and  in  these  the 
young  are  protected  until  they  hatch.     In  the  limpets  and 
many  of  the  chitons  the  eggs  are  laid  by  thousands  directly 
in  the  water,  and  after  a  short  time  develop  into  free-swim- 
ming young,  differing  considerably  from  the  parent  in  ap- 
pearance.   Those  escaping  the  ravages  of  numerous  enemies 
finally  settle  down  in  a  favorable  situation  and  gradually 
assume  the  form  of  the  adult. 

89.  Age,  enemies,  and  means  of  defense  of  lamellibranchs 
and  gasteropods. — How  much  time  is  consumed  by  the  young 
in  growing  up,  and  the  length  of  time  they  live,  are  ques- 
tions generally  unsettled.    It  is  said  that  the  oyster  requires 
five  years  to  attain  maturity,  and  lives  ten  years  ;  the  fresh- 
water clam  develops  in  five  years,  and  some  species  live  from 


MOLLtTSKS  87 

twelve  to  thirty  years ;  and  the  average  length  of  life  of 
the  snail  appears  to  be  from  two  to  five  years.  Certain  it 
is  that  mollusks  have  numerous  enemies  besides  man  which 
prevent  multitudes  from  living  lives  of  normal  length. 
Birds,  fishes,  frogs,  and  starfishes  beset  them  continually, 
and  many  fall  a  prey  to  the  ravages  of  internal  parasites  or 
to  other  mollusks.  Under  ordinary  circumstances  the  shell 
is  sufficient  protection,  and  the  spines  disposed  on  the  sur- 
face in  many  species  render  the  occupant  still  less  liable  to 
attack.  Many  snails  carry  on  the  foot  a  horny  or  calcare- 
ous plate  known  as  the  operculum,  which  closes  the  en- 
trance of  the  shell  like  a  door  against  intruders.  Certain 
noxious  secretions  poured  out  from  the  skin  also  serve  as  a 
means  of  defense,  and  many  Xudibranchs  (Fig.  50)  bear 
nettle-cells  on  the  processes  of  the  body,  which  probably 
render  them  distasteful  to  many  animals.  Finally,  there 
are  numerous  clams,  mussels,  snails,  and  slugs  whose  colors 
harmonize  so  closely  with  their  surroundings  that  they  al- 
most completely  baffle  detection,  and  enable  them  to  lead 
as  successful  a  life  as  those  provided  with  special  organs  of 
defense. 

90.  Cephalopods. — The  animals  belonging  to  this  class, 
such  as  the  -squids  and  cuttlefishes  (Fig.  52),  are  by  far 
the  most  highly  developed  mollusks.  They  are  of  great 
strength,  capable  of  very  rapid  movements,  and  several  spe- 
cies are  many  times  the  largest  invertebrates.  In  almost 
every  case  there  is  a  well-defined  head  bearing  remarkably 
perfect  eyes,  and  also  a  circle  of  powerful  arms  provided 
with  numerous  suckers  which  aid  in  the  capture  of  food 
(Fig.  52).  Posteriorly  the  body  is  developed  into  a  pointed 
or  rounded  visceral  mass  which  to  a  certain  extent  is  free 
from  the  head,  giving  rise  to  a  well-marked  neck.  Some 
forms,  such  as  the  squids  (Fig.  52,  upper  figure),  are  pro- 
vided with  fins  which  drive  the  animal  forward,  but  in  com- 
mon with  other  cephalopods  they  are  capable  of  a  very  rapid 
backward  motion.  By  muscular  movements  water  is  taken 


88 


ANIMAL  FORMS 


into  the  large  mantle  cavity  within  the  body,  a  set  of  valves 
prevents  its  exit  through  the  same  channels,  and  upon  a 
vigorous  contraction  of  the  body  walls  the  water  is  forced 
out  rapidly  through  the  small  opening  of  the  funnel,  which 


FIQ.  52. — Cephalopods.  Lower  figure,  the  devil-fish  or  octopus  (Octopus  jninctatm). 
The  upper  figure  represents  the  squid  (Loligo  pealii)  swimming  backward  by 
driving  a  stream  of  water  through  the  small  tube  slightly  beneath  the  eyes.  From 
life,  one-third  natural  size. 

drives  the  animal  backward  after  the  fashion  of  an  explod- 
ing sky-rocket.  In  this  way  they  usually  escape  the  fishes 
and  whales  that  prey  upon  them,  but  an  additional  device 
has  been  provided  in  the  form  of  a  sac  within  the  body, 
whose  inky  contents  may  be  liberated  in  such  quantity  as 
to  cloud  the  water  for  a  considerable  distance,  and  thus 
enable  them  to  slip  away  unseen  into  some  place  of  safety. 
Most  of  the  cephalopods  are  further  protected  by  their 
ability  to  assume,  like  the  chameleon,  the  color  of  the  object 


MOLLUSKS  89 

upon  which  they  rest.  In  the  skin  are  embedded  multi- 
tudes of  small  spherical  sacs  filled  with  pigments  of  various 
colors,  chiefly  shades  of  red,  brown,  and  blue,  each  sac  be- 
ing connected  with  a  nerve  and  a  series  of  delicate  muscles. 
If  the  animal  settles  upon  a  red  surface,  for  example,  a 
nerve  impulse  is  sent  to  each  of  the  hundreds  of  color  sacs 
of  corresponding  shade,  causing  the  muscles  to  contract 
and  flatten  the  bag  like  a  coin,  and  thus  exposing  a  far 
greater  surface  than  before,  they^give  the  animal  a  reddish 
hue.  In  the  twinkling  of  an  eye  they  may  completely 
change  to  another  tint,  or  present  a  mottled  look,  and  some 
may  even  throw  the  surface  of  the  skin  into  numerous 
small  projections  that  make  the  animal  appear  part  of  the 
rock  upon  which  it  rests.  These  devices  not  only  serve  for 
protection,  but  they  also  aid  in  enabling  these  mollusks  to 
steal  upon  their  prey,  chiefly  fishes,  which  they  destroy  in 
great  numbers  with  lionlike  ferocity. 

The  devil-fishes  and  a  number  of  other  species  are  usu- 
ally found  creeping  along  the  sea  bottom,  generally  near 
shore,  and  are  solitary  in  their  habits,  while  the  squids  re- 
main near  the  surface  and  frequently  travel  in  great  com- 
panies, sometimes  numbering  hundreds  of  thousands.  In 
size  they  usually  range  from  a  few  inches  to  a  foot  or  two 
in  length,  but  a  few  devil-fishes  and  squids  attain  a  greater 
size,  some  of  the  latter  reaching  the  enormous  length  of 
from  forty  to  sixty  feet.  There  are  many  stories  of  their 
great  strength  and  of  their  voluntarily  attacking  people 
and  even  overturning  boats,  but  the  latter  are  in  almost 
every  case  sailors'  yarns. 

In  their  external  organization  the  cephalopods  have 
little  to  remind  one  of  any  of  the  preceding  mollusks,  and 
their  internal  structure  shows  only  a  distant  resemblance. 
In  the  Octopi  (Fig.  52)  the  shell  is  lacking  ;  in  the  squid  it 
is  called  the  pen,  and  consists  of  a  horn-like  substance  with- 
out any  lime  deposit ;  in  the  cuttlefishes  it  is  spongy  and 
plate-like,  and  is  a  familiar  object  in  the  shops  ;  and,  finally, 


90  ANIMAL  FORMS 

in  the  nautilus  it  is  coiled  and  of  considerable  size,  and,  un- 
like that  of  any  other  cephalopod,  it  is  carried  on  the  out- 
side of  the  animal.  Interiorly  it  is  divided  by  a  number  of 
partitions  into  chambers,  the  last  one  of  which  is  occupied 
by  the  animal. 

The  alimentary  canal  shows  some  resemblance  to  that 
of  other  mollusks,  but,  as  in  the  case  of  the  other  systems 
of  the  body,  it  possesses  a  far  higher  state  of  development. 
The  mouth  is  situated  in  the  center  of  a  circle  of  arms, 
which  in  reality  are  modified  portions  of  the  foot,  and  is 
furnished  with  two  parrot-like  jaws.  From  this  point  the 
esophagus  leads  back  into  the  body  mass  to  the  stomach, 
which  with  the  liver  and  intestine  are  sufficiently  like 
those  of  the  clam  and  snail  to  require  no  further  comment. 

Eespiration  is  effected  by  the  skin  to  a  certain  extent, 
but  chiefly  by  two  gills  (four  in  the  nautilus),  and  the  cir- 
culatory system,  which  conveys  the  blood  to  and  from  these 
organs  and  over  the  body  with  its  complex  heart,  arteries, 
capillaries,  and  veins,  is  more  highly  developed  than  in 
any  other  invertebrate. 

As  might  be  expected  in  animals  with  so  great  sagacity 
and  cunning,  the  nervous  system  of  the  sense-organs  reach 
a  degree  of  development  but  little  short  of  what  we  find  in 
some  of  the  vertebrates.  The  chief  part  of  the  nervous 
system  is  located  in  the  head,  protected  by  a  cartilaginous 
skull,  a  very  rare  structure  among  invertebrates ;  and  while 
the  different  ganglia  may  be  recognized  in  a  general  way 
and  be  found  to  correspond  to  a  certain  extent  to  those 
of  foregoing  mollusks,  they  are  so  largely  developed  and 
massed  together  that  it  is  impossible  at  present  to  under- 
stand them  fully.  From  this  point  nerves  pass  to  all 
regions  of  the  body,  to  the  powerful  muscles,  the  viscera, 
and  the  organs  of  special  sense,  controlling  the  complex 
mechanism  in  all  its  workings. 

There  is  no  doubt  that  the  cephalopods  see  distinctly 
for  considerable  distances,  and  a  careful  examination  of 


MOLLUSKS  91 

the  eye  of  the  squids  and  cuttlefishes  has  shown  them 
to  be  remarkably  complex  and  in  many  respects  to  be 
constructed  upon  much  the  same  plan  as  those  of  the 
vertebrates.  As  to  the  other  senses  not  so  much  is  known, 
but  undoubtedly  many  species  of  cephalopods  are  possessed 
of  a  shrewdness  and  cunning  not  shared  by  any  other 
invertebrates,  save  some  of  the  insects  and  spiders,  and  are 
vastly  more  highly  organized  than  their  molluscan  rela- 
tives. 

91.  How  species  originate.— We  have  now  examined  a 
considerable  portion  of  the  animal  kingdom,  tracing  its 
members  from  their  simplest  beginnings  as  single  cells, 
through  the  formation  of  colonial  types,  and  up  through 
the  sponges,  ccelenterates,  worms,  and  mollusks.  It  is  im- 
portant once  more  to  note  that  they  all  perform  the  func- 
tions concerned  in  nutrition  and  reproduction,  and  only 
these.  The  differences  which  exist  are  those  of  structure. 
The  Hydra  and  the  clam,  for  example,  perform  the  same 
duties,  but  their  bodily  apparatus  differs  widely,  and  the 
completeness  and  perfection  of  the  work  varies  accord- 
ingly. The  more  the  work  to  be  performed  by  an  organ- 
ism is  divided  up  among  especially  adapted  organs,  so  that 
each  of  the  latter  has,  as  far  as  possible,  only  one  thing  to 
do,  the  higher  is  the  organism. 

As  stated  earlier  in  the  account,  it  is  believed  that  the 
more  complex  animals  arose  from  the  simpler ;  that  if  we 
could  trace  the  history  of  any  of  the  great  groups  back 
toward  their  first  beginnings,  we  would  find  them  all  to 
have  originated  from  one  ancestral  form,  that  in  turn  owes 
its  descent  from  yet  simpler  forms. 

Let  us  see  something  of  how  this  has  come  about.  We 
all  know  that  vast  numbers  of  young  are  born  into  this 
world  which  never  come  to  maturity.  It  is  said  that  if  all 
the  young  of  the  codfish  were  to  live  their  allotted  time, 
it  would  be  less  than  fifteen  years  before  the  sea  would 
become  literally  packed  with  them.  Numerous  enemies, 


92  ANIMAL   FORMS 

the  lack  of  food,  and  other  agencies  annihilate  the  larger 
part.  We  also  know  that  no  two  offspring  are  exactly 
alike.  They  exhibit  individual  differences.  One  bird  may 
have  a  larger  bill  than  another  of  the  same  brood  which 
excels  in  length  of  wing.  As  noted  above,  all  the  offspring 
will  not  attain  maturity.  Those  best  adapted  to  their  sur- 
roundings will  have  the  best  chances  of  survival.  The 
increased  length  of  bill  or  wing  may  be. slight,  but  it  may 
be  just  this  amount  which  enables  the  bird  to  probe  deeper 
or  fly  farther  and  thus  secure  the  requisite  amount  of  food. 
A  premium  is  placed  on  length  of  wing  or  bill  generation 
after  generation,  with  the  result  that  a  long-billed  species 
arises  distinct  from  the  long-winged  which  trace  their 
ancestry  back  to  the  same  parents.  It  is  the  same  prin- 
ciple which  enables  the  breeder  to  increase  the  swiftness 
of  the  race-horse  and  the  strength  of  the  draft-horse,  or 
the  gardener  to  develop  from  the  wild  rose  the  great  num- 
ber of  widely  different  varieties.  In  the  same  way  other 
slight  peculiarities  over  very  many  generations  may  en- 
.able  other  forms  to  gradually  adapt  themselves  to  still  dif- 
ferent modes  of  life.  Thus  vast  numbers  of  organisms 
gradually  become  modified  in  form  and  complexity,  and 
are  adapted  to  lives  which  insure  them  a  comparative 
degree  of  safety  and  less  competition  with  other  species. 


CHAPTER  IX 

ARTHROPODS.   CLASS  CRUSTACEA 

92.  General  characters. — In  the  Arthropods,  that  is,  the 
crabs,  lobsters,  shrimps,  insects,  spiders,  and  a  vast  host 
of  related  forms,  the  body  is  bilaterally  symmetrical,  and 
is  composed  of  a  number  of  segments  arranged  in  a  series, 
as  in  the  earthworm  and  other  annelids.     A  hornlike  cu- 
ticle, sometimes  called  the  shell,  bounds  the  external  sur- 
face— in  early  life  thin  and  delicate,  but  later  relatively 
thick,  and  often  further  strengthened  by  lime  salts.   Along 
the  line  between  the  segments  this  coat  of  mail  remains 
thin  and  forms  a  flexible  joint.    Appendages  also  are  borne 
on  each  segment,  not  comparatively  short  and  fleshy  out- 
growths like  the  lateral  appendages  of  many  of  the  worms, 
but  usually  long  and  jointed  (hence  the  name  Arthropod, 
meaning  jointed  foot),  and  variously  modified  for  many 
different  uses. 

93.  Classification. — The  species  belonging  to  this  group 
outnumber  the  remainder  of  the  animal  kingdom.     Their 
haunts  also  are  most  diverse.     Some  are  adapted  for  lives 
in  the  sea  and  fresh  water,  others  for  widely  different  sit- 
uations on  land,  and  a  great  number  are  constructed  for  a 
life  on  the  wing.    A  certain  resemblance  exists  among  them 
all,  but  the  modifications  which  fit  them  for  their  different 
habitats  are  also  profound,  and  have  resulted  in  the  division 
of  the  Arthropods  into  five  classes.     The  first  class  ( Crus- 
tacea) contains  the  crayfish,  crabs,  etc.  ;  the  second  (Ony- 
chophora)  includes  the  curious  worm-like  peripatus  (Fig. 

93 


94  ANIMAL  FORMS 

66);  the  third  (Myriapoda,  meaning  myriad-footed)  em- 
braces the  centipeds  and  "thousand-legs";  the  fourth  (In- 
secta]  contains  the  insects;  and  the  fifth  (Arachnida)  in- 
cludes the  scorpions,  spiders,  and  mites. 

94.  The  Crustacea. — The   number  of  species  of  crusta- 
ceans is  estimated  to  be  about  ten  thousand,  and  while  the 
greater  number  of  these  are  marine,  many  are  found  in 
fresh  water  and  a  few  occur  on  land.     In  size  they  range 
from  almost  microscopic   forms  to  the  giant   crabs  and 
lobsters.     They  differ  also  in  shape  to  a  remarkable  degree, 
but  at  the  same  time  there  is  a  decided  resemblance  through- 
out the  group,  except  in  those  species  which  have  become 
modified  by  a  parasitic  habit.     The  characteristic  external 
skeleton  is  invariably  present,  and  gives  evidence  of  the 
deep  internal  segmentation   of  the  body.     In  the  simple 
Crustacea  this  is  very  apparent,  but  in  the  higher  forms  it 
is  usually  more  or  less  obscured,  owing  to  the  fusion  of  some 
of  the  different  segments,  especially  those  of  the  head,  as  in 
the  crayfish  (Fig.  59). 

The  class  of  the  Crustacea  is  subdivided  into  two  sub- 
classes (Entomostraca  and  Malacostraca),  the  first  containing 
the  fairy-shrimps  (Branchipus,  Fig.  53)  and  their  allies,  the 
copepods  (such  as  Fig.  54),  the  barnacles  (Fig.  55),  and  a 
number  of  other  species.  In  their  organization  all  are  com- 
paratively simple,  usually  small,  and  the  appendages  show 
relatively  little  specialization.  The  other  subclass  contains 
the  more  highly  developed  and  usually  large-sized  Crustacea, 
among  which  are  the  shrimps,  crayfishes,  lobsters,  crabs, 
and  a  number  of  other  forms. 

95.  Some  simple  Crustacea. — While  the  members  of  the 
first  subclass  are  minute  and  inconspicuous,  several  species 
are  often  remarkably  abundant  in  our  small  fresh-water 
pools.    Among  these  is  the  beautifully  colored  fairy-shrimp 
(Branchipus,  Fig.  53),  with  greatly  elongated  body  and 
leaf-like  appendages,  whose  relatively  simple  character  leads 
the  zoologist  to  think  that  they  are  among  the  simplest 


ARTHROPODS.      CLASS  CRUSTACEA  95 

Crustacea,  and  in  several  points  resemble  the  ancestral  form 
from  which  all  the  modern  species  have  descended.  Some 
nearly  related  forms  are  provided  with  a  great  fold  of  the 
body-wall,  which  may  almost  completely  conceal  the  animal 
from  above,  or  it  may  be  formed  like  a  bivalve  clam-shell, 
within  which  the  entire  body  may  be  withdrawn.  This 


FIG.  53.— Fairy-shrimp  (Branchipvs).  b,  brood-pouch  ;  <?,  e', 
compound  and  simple  eyes ;  /,  paddle-shaped  feet ;  h,  tu- 
bular heart ;  i,  intestine. 


latter  character  is  also  found  in  the  water-fleas  (Daphnia), 
very  much  smaller  forms,  and  sometimes  occurring  in  mil- 
lions on  the  bottoms  of  our  ponds  and  marshes.  They  are 
readily  distinguished  from  the  fairy-shrimp  by  the  short- 
ness of  the  body,  the  small  number  of  appendages,  and  by 
their  habit  of  using  their  antennae  as  swimming  organs, 
which  gives  to  their  locomotion  a  jerky,  awkward  character. 
96.  Cyclops  and  relatives. —  Cyclops  (Fig.  54),  the  repre- 
sentative of  a  number  of  lowly  forms  belonging  to  the  order 
of  Copepods,  is  one  of  the  commonest  fresh-water  Crustacea. 
The  forward  segments  of  the  spindle-shaped  body  are  cov- 
ered by  a  large  shield  or  carapace,  the  feet  are  few  in  num- 
ber, and,  like  its  fabled  namesake,  it  bears  an  eye  in  the 
center  of  the  forehead.  Nearly  related  species  are  also  re- 
markably abundant  at  the  surface  of  the  sea,  at  times  occur- 


ANIMAL   FORMS 


ring  in  such  vast  numbers  that  they  impart  a  reddish  tinge 
to  the  water  over  wide  areas,  and  at  night  are  largely  re- 
sponsible for  its  phos- 
phorescence. Many  oth- 
ers are  parasitic  in  their 
habits,  and  scarcely  a 
salt-water  fish  exists  but 
that  at  one  time  or  an- 
other suffers  from  their 
attacks.  On  the  other 
hand,  many  fresh-  and 
salt-water  fishes  depend 
upon  the  free-swimming 
forms  for  food,  and 
hence,  from  an  economic 
point  of  view,  they  are 
highly  important  organ- 
isms. 

97.  Barnacles.  —  The 
parasitic  habit  and  the 
lack  of  locomotion  has 
also  produced  marvelous 
changes  among  the  bar- 
nacles, so  great  that 
originally  they  were 
placed  among  the  mol- 
lusks ;  and  as  with  the  parasitic  copepods,  their  true  posi- 
tion was  only  known  after  their  life-history  had  been  de- 
termined. In  the  goose-barnacles  *  the  body,  attached  by 
a  fleshy  stalk  to  foreign  objects,  is  enclosed  by  a  tough 
membrane,  corresponding  to  the  carapace  of  other  Crus- 
tacea, in  which  are  embedded  five  calcareous  plates.  This 


FIG.  54. — Cyclops,     e.  s.,  eggs  ;  i,  intestine 
reproductive  organ. 


*  So  called  because  of  the  belief,  which  existed  for  three  hundred 
years  prior  to  the  present  century,  that  when  mature  these  animals 
give  birth  to  geese. 


ARTHROPODS.      CLASS  CRUSTACEA 


97 


is  open  along  one  side,  and  allows  the  feather-like  feet  to 
project  and  produce  currents  in  the  surrounding  water 
which  brings  food  within  reach.  In  the  acorn-barnacles 
(Fig.  55)  the  stalk  is  absent,  and  the  body,  though  possess- 


FIG.  55. — Barnacles.    Acorn-barnacles  chiefly  in  lower  part  of  figure  ;  goose-barnacles 
above.    Natural  size. 

ing  the  same  general  character  as  the  goose-barnacles,  is 
shorter,  and  enclosed  in  a  strong  palisade  consisting  of  six 
calcareous  plates. 

The  larger  number  of  barnacles  attach  themselves  to 
the  supports  of  wharves,  the  hulls  of  ships,  floating  tim- 
bers, the  rocks  from  the  shore-line  down  to  considerable 
depth,  and  a  few  species  occur  on  the  skin  of  sharks  and 
whales.  On  the  other  hand,  there  are  severaLspecies  which 
are  parasitic,  and  in  accordance  with  this  mode  of  life  ex- 
hibit various  degrees  of  degeneration.  In  the  most  extreme 


98  ANIMAL  FORMS 

cases  (Sacculina)  the  sac-like  body,  attached  to  the  abdo- 
men of  crabs,  is  entirely  devoid  of  appendages  and  any 
signs  of  segmentation.  A  root-like  system  of  delicate  fila- 
ments extends  from  the  exposed  part  of  the  animal  into 
the  host  and  absorbs  the  necessary  nutriment.  The  mouth 
and  alimentary  canal  are  accordingly  absent — in  fact,  the 
body  contains  little  but  the  reproductive  organs  and  a  very 
simple  nervous  system. 

98.  Structure. — In  the   internal    organization   of   these 
smaller  crustaceans  many  differences  may  be  noted,  though 
they  are  usually  less  profound  than  the  external.     Ordi- 
narily  the-  alimentary   canal    is   a   straight    tube   passing 
through    the    body,  and    is    provided   with   a    pouch-like 
stomach,  and   a   more  or  less   clearly  defined   liver.     In 
all,  except  the  parasitic  species,  the  external  mouth-ap- 
pendages masticate  the  food,  and  in  a  very  few  of  the 
above-described  groups  it  may  be  further  ground  between 
the  horny  ridges  on  the   stomach-walls.     After  this  pre- 
liminary treatment  it  is  subjected   to  the  action  of  the 
digestive  juices,  and  when  liquefied  is  absorbed  into  the 
body.     Here  it  is  circulated  by  a  blood-system  of  widely 
different  character.     In  many  cases  definite  arteries  and 
veins  are  absent.     The  blood  courses  through  the  body  in 
the  spaces  between  the  different  organs  propelled  by  the 
beating  of  the  heart,  which  it  is  made  to  traverse.     In 
Cyclops  (Fig.  54)  even  the  heart  is  absent,  and  the  blood 
is  made  to  circulate  by  contractions  of  the  intestine.     In 
most  of  these  smaller  Crustacea  considerable  oxygen  is  ab- 
sorbed through  the  body-wall ;  but  in  several  species,  for 
example,  the  fairy-shrimp  (Fig.  53),  special  gills  are  devel- 
oped on  the  appendages  of  the  body. 

99.  Multiplication. — Among  the  Crustacea  thus  far  con- 
sidered the  males  are  usually  readily  recognized  owing  to 
their  small   size.     The  females  also  are  usually  provided 
with  brood-pouches  in  which  the  developing  eggs  are  pro- 
tected.    In  almost  every  case  the  young  are  born  in  the 


ARTHROPODS.     CLASS  CRUSTACEA 


99 


form  of  minute  larvae,  provided  with  three  pairs  of  append- 
ages, a  median  eye  (Fig.  56),  and  a  firm  external  skeleton 
or  cuticle.  This  latter  prevents  the  continuous  growth  of 
the  larvae  or  nauplius,  and  every  few  days  it  is  thrown  off, 
and  while  the  new  one  is  forming  the  body  enlarges.  Dur- 
ing this  time  new  appendages  are  developed,  so  that  after 
each  moult  the  young  crusta- 
cean emerges  less  like  its 
former  self  and  more  and  more 
like  its  parents.  In  the  bar- 
nacles, after  several  moults 
have  taken  place,  the  young 
become  permanently  attached 
by  means  of  their  first  anten- 
nae, their  thoracic  feet  change 
into  feathery  appendages,  and 
several  other  changes  occur. 
In  some  of  the  parasitic  bar- 
nacles (Sacculina)  the  larva 
attaches  itself  to  a  crab,  throws 
off  its  various  appendages,  and, 
after  other  great  degenerative 
changes,  enters  its  host.  For 
a  time,  therefore,  their  development  is  toward  greater  com- 
plexity, but  the  later  stages  constitute  a  retrograde  meta- 
morphosis. 

100.  More  complex  types.— The  larger,  more  useful,  and 
usually  more  familiar  Crustacea  belong  to  the  second  divi- 
sion (subclass  Malacostraca).  It  comprises  such  animals  as 
the  shrimps,  crayfish,  lobsters,  crabs,  and  a  number  of  other 
forms  which  are  at  once  distinguished  from  the  preceding 
by  the  constant  number  of  segments  composing  the  body. 
Of  these,  five  constitute  the  head,  eight  the  thorax,  and 
seven  the  abdomen.  The  head  segments  are  always  fused 
together,  and  with  them  one  or  more  thoracic  segments 
unite  to  form  a  more  or  less  complete  cephalothorax.  Also, 


FIG.  56.— Development  of  a  barnacle 
(Lepas).    a,  larva  ;  b,  adult. 


100  ANIMAL  FORMS 

some  of  the  head  segments  give  rise  to  a  great  fold  of  the 
body-wall,  the  carapace,  which  extends  backward  and  covers 
all  or  a  part  of  the  thorax,  with  which  it  may  firmly  unite, 
as  in  the  crayfish.  The  appendages  are  usually  highly  spe- 
cialized, and  are  made  to  perform  a  variety  of  functions. 

101.  The  shrimps. — Among  the  simplest  of  these  are  the 
opossum-shrimps  (Fig.  57)  and  their  relatives,  small  trans- 


FIG.  57.— The  opossum-shrimp  (Mysis  americana). 

parent  creatures  often  seen  swimming  in  great  numbers  at 
the  surface  of  the  sea  or  hiding  among  the  seaweeds  along 
the  shore.  In  general  appearance  they  resemble  crayfishes 
or  prawns,  but  are  readily  distinguished  by  the  two-branched 
thoracic  feet.  This  "  split-foot "  character  also  occurs 
among  many  of  the  preceding  Crustacea,  and  is  generally 
a  badge  of  low  organization,  tending  to  disappear  in  the 
more  highly  organized  forms.  In  this  and  other  respects 
the  shrimps  are  especially  interesting  in  their  relation  to 
the  preceding  Crustacea,  and  in  the  fact  that  they  may 
closely  resemble  the  ancestors  of  the  modern  prawns  (Fig. 
58),  lobsters,  crayfishes,  and  crabs. 

102.  Crayfishes  and  lobsters. — The  last-mentioned  spe- 
cies and  their  allies,  usually  large  and  familiar  forms,  con- 
stitute a  group  known  as  the  decapods  (meaning  ten  feet), 
referring  to  the  number  of  thoracic  feet.  Among  the  mem- 
bers of  this  division  probably  none  are  more  familiar  than 
the  crayfishes,  which  occur  in  most  of  the  larger  rivers  and 
their'tributaries  throughout  the  United  States  and  Europe.  \ 
It  is  their  habit  to  remain  concealed  in  crevices  of  rocks 


ARTHROPODS.     CLASS  CRUSTACEA 


101 


or  in  the  mouths  of  the  burrows  which  they  excavate,  and 
from  which  they  rush  upon  the  small  fish,  the  larvae  of 


FIG.  58.— Prawn  (Heplacarpus  brevirostris). 

many   animals,  and    other    equally   defenseless    creatures 
which   constitute   their  bill   of   fare.      In   turn   they  are 
eagerly  sought  by  certain  birds  and  four-footed  animals,  and, 
especially     in     France, 
are  extensively  used  for 
food  by  man. 

Closely  related  to 
.the  crayfishes  and  dif- 
fering but  little  from 
them  structurally  are 
the  lobsters.  In  this 
country  they  are  con- 
fined to  the  rocky  coasts 
from  Xew  Jersey  to 
Labrador,  living  upon 
fish,  fresh  or  otherwise, 
various  invertebrates, 
and  occasionally  sea- 
weeds. Far  more  than 
the  crayfish,  the  lobster 
is  in  demand  as  an  arti- 
cle of  food.  By  the  aid 

Of  nets   or  Various  traps  FIG.  59.— The  crayfish  (Astacus). 


102  ANIMAL  FORMS 

millions  are  caught  each,  year,  and  to  such  an  extent  has 
their  destruction  proceeded  that  in  many  places  they  are 
well-nigh  exterminated.  At  the  present  time,  however,  leg- 
islation, numerous  hatcheries,  and  a  careful  study  of  their 
life  habits  is  doing  much  to  better  matters  and  inciden- 
tally to  put  us  in  possession  of  many  interesting  zoological 
facts  along  this  line,  some  of  which  will  be  mentioned  later. 
Frequently  the  prawns,  especially  the  larger  ones,  and  a 
spiny  lobster  (Palinurus),  are  mistaken  for  crayfishes  or 
lobsters,  but  they  differ  from  them  in  the  absence  of  the 
large  grasping  claws. 

Along  almost  any  coast  some  of  these  animals  are  to  be 
found,  often  beautifully  colored  and  harmonizing  with  the 
seaweeds  among  which  they  live,  or  so  transparent  that 
their  internal  organization  may  be  distinctly  seen.  Farther 
out  at  sea  other  species  swim  in  incredible  numbers,  feed- 
ing upon  minute  organisms,  and  in  turn  fed  upon  by  numer- 
ous fishes  and  whales ;  and,  especially  on  the  Pacific  coast, 
shrimp-fishing  is  an  important  industry. 

103.  The  hermit-crabs. — The  last  of  these  long-tailed 
decapods  is  the  interesting  group  of  the  hermit-crabs, 
which  occur  in  various  situations  in  the  sea.  In  early  life 
they  take  possession  of  the  empty  shell  of  some  snail,  and 
the  protected  abdomen  becomes  soft  and  flabby,  while  the 
appendages  in  this  region  almost  completely  disappear. 
The  front  part  of  the  body,  on  the  other  hand,  continually 
grows  in  firmness  and  strength,  and  is  admirably  adapted 
for  the  continual  warfare  which  these  forms  wage  among 
themselves.  As  growth  proceeds  the  necessity  arises  for  a 
larger  shell,  and  the  crab  goes  "house-hunting"  among  the 
empty  shells  along  the  shore,  or  it  may  forcibly  extract  the 
snail  or  other  hermit  from  the  home  which  strikes  its- fancy. 

Many  of  the  hermit-crabs  enjoy  immunity  from  the 
attacks  of  their  belligerent  relatives  by  allowing  various 
hydroids  to  grow  upon  their  homes.  Others  attach  sea- 
anemones  to  their  shells  or  to  one  of  their  large  claws, 


ARTHROPODS.      CLASS  CRUSTACEA 


103 


which  they  poke  into  the  face  of  any  intruder.     While 
the  anemones  or  hydroids  are  made  to  do  valiant  service 


FIG.  60.— Hermit-crab  (Pagurus  bernhardus)  in  snail  shell  covered  with  Hydractima. 

with  their  nettle-cells,  they  also  enjoy  the  advantages  of 
a  large  food-supply  which  is  attendant  upon  the  free  ride. 

104.  The  crabs. — The  most  highly  developed  Crustacea 
are  the  crabs  or  short-tailed  decapods  which  abound  between 
tide-marks  alongshore,  and  in  diminishing  numbers  extend 
to  great  depths.  The  cephalothorax  is  usually  relatively 
wide,  often  wider  than  long,  and  the  greatly  reduced  abdo- 
men is  folded  against  the  under  side  of  the  thorax.  Corre- 
lated with  the  small  size  of  the  abdomen,  the  appendages 
of  that  region  disappear  more  or  less,  but  the  remaining 
appendages  are  similar  to  those  of  the  crayfish  or  lobsters. 
All  these  different  parts,  however,  are  variously  modified  in 
each  species  to  fit  it  for  its  own  peculiar  mode  of  life.  In 
some  forms,  such  as  the  common  cancer-crab  (Fig.  61),  the 
legs  are  comparatively  thick-set  and  possessed  of  great 
strength,  enabling  them  to  defend  themselves  against  most 
enemies.  On  the  other  hand,  there  are  the  spider-crabs 
with  small  bodies  and  relatively  long  legs,  withal  weak,  and 


104: 


ANIMAL  FORMS 


yet  so  harmonizing  with  their  surroundings  that  they  are 
as  likely  to  survive  as  their  stronger  relatives.     In  this 


Fio.  61.— Kelp-crab  (Epialtus  productus)  in  upper  part  of  figure ;  to  the  right  the 
edible  crab  (Cancer  productus),  and  the  shore-crab  (Pugettia  richii). 

connection  it  is  interesting  to  note  that  the  giant  crab  of 
Japan,  the  largest  crustacean,  being  upward  of  twenty  feet 
from  tip  to  tip  of  the  legs,  is  a  spider-crab,  constructed  on 


FIG.  62.— The  fiddler-crab  (Gelasimtu).    Photograph  by  Miss  MABV  RATHBUS. 

the   same  general  pattern  as  our   common   coast  forms. 
Between  these  two  extremes  numberless  variations  exist, 


ARTHROPODS.      CLASS  CRUSTACEA 


105 


some  for  known  reasons,  biit  more  often  not  readily  under- 
stood. And  not  only  does  the  form  vary,  but  the  external 
surface  may  be  sculptured  or  beset  with  spines  or  tubercles 
which  frequently  render  the  animal  inconspicuous  amid  its 
natural  surroundings.  Such  an  effect  is  heightened  by  the 
presence  of  sponges,  hydroids,  and  various  seaweeds  which 
the  crab  often  permits  to  gather  upon  its  body. 

105.  Pill-bugs  and  sandhoppers. — Finally  there  remain  the 
groups  of  the  pill-  or  sow-bugs  (Isopods)  and  the  sand-fleas 
or  sandhoppers  (Amphipods).  In  the  first  of  these  the 
body  is  usually  small  and  compressed,  the  thorax  more  or 
less  plainly  segmented,  and  the  seven  walking  (thoracic) 
legs  are  similar.  In  the  female  each  leg  bears  at  its  base  a 
thin  membranous  plate  which  extends  inward  and  hori- 


FIG.  63. — Isopod  or  pill-bug  (Porcellio  laevis). 

zontally,  thus  forming  on  the  under  side  of  the  body  a 
brood-pouch  (Fig.  63)  in  which  the  young  develop.  As 
one  may  readily  discover  in  any  of  the  common  species, 
the  abdominal  segments  are  more  or  less  fused,  and  bear 
appendages  adapted  for  respiration  and,  in  the  aquatic 
forms,  for  swimming. 


106 


ANIMAL  FORMS 


The  marine  isopods  occur  in  the  sand,  under  rocks,  and 
in  the  seaweeds ;  many  are  parasitic  upon  fishes ;  and  the  ter- 
restrial forms  (Fig.  63)  are  very  common  objects  under  old 


FIG.  64.— Amphipods  or  sand-fleas  (Gammarm,  upper  species,  and  Caprella). 

logs  and  in  cellars,  where  they  live  chiefly  on  vegetable  mat- 
ter. In  the  sand-fleas  the  body  is  compressed  from  side  to 
side,  and  while  the  thorax  shows  distinct  segments,  the  legs 
are  frequently  dissimilar,  and  some  may  bear  pincers.  One 
of  their  most  distinctive  marks  concerns  the  last  three  ab- 
dominal appendages,  which  are  usually  modified  for  leaping. 
The  sand-fleas  (Fig.  64)  are  familiar  objects  to  any  one 
who  has  collected  along  the  beach  and  has  turned  over  the 
cast-up  seaweeds,  while  numbers  of  small  species  often  oc- 
cur among  the  plants  in  our  fresh-water  ponds.  Some  most 
curious  and  highly  modified  forms,  whose  general  appear- 
ance is  shown  in  the  lower  part  of  Fig.  64,  occur  among 


ARTHROPODS.      CLASS  CRUSTACEA  107 

hydroid  colonies,  with  which  their  bodies  harmonize  in 
form  and  color.  And,  lastly,  most  bizarre  creatures,  known 
as  "  whale-lice,"  attach  themselves  to  the  skin  of  whales,  of 
which  each  species  acts  as  host  for  one  or  more  kinds. 

106.  Internal  organization.— Most  Crustacea  are  carnivo- 
rous, preying  upon  almost  any  of  the  smaller  animals  within 
convenient  reach ;  a  much  smaller  number  live  on  vege- 
table food ;  and  there  are  many,  such  as  the  crayfishes,  lob- 
sters, and  numerous  crabs,  which  are  also  notorious  scaven- 
gers. In  these  latter  forms  the  food  is  held  in  one  of  the 
large  pincers,  torn  into  shreds  by  the  other,  and  transferred 
to  the  mouth-parts,  where,  as  in  all  Crustacea,  it  is  soon 
reduced  to  a  pulp  by  their  rapid  movements.  In  many 
species  the  food  is  now  ready  for  the  digestive  process, 
but  not  so  in  the  higher  forms.  If  the  stomach  of  any  of 
these,  for  example,  the  crabs  or  crayfishes,  be  opened,  three 
(Fig.  65,  *)  large  teeth  operated  by  powerful  muscles  will 
be  noted,  and  beyond  these  a  strainer  consisting  of  many 
closely  set  hairs.  In  operation  this  "  gastric  mill "  takes 
the  food  passed  on  from  the  mouth-parts,  and  crushes  and 
tears  it  until  fine  enough  to  pass  through  the  strainer, 
whereupon  it  is  dissolved  by  the  juices  from  the  liver  and 
is  absorbed  as  it  passes  down  the  intestine. 

The  circulatory  system  is  usually  highly  developed,  and 
consists  of  a  heart,  in  some  species  almost  as  long  as  the 
body,  though  usually  shorter  (Fig.  65),  from  which  two  or 
more  arteries  branch  to  all  parts  of  the  body.  Here  the 
blood,  instead  of  emptying  into  definite  veins,  pours  into  a 
series  of  spaces  or  sinuses  in  among  the  muscles  and  other 
organs  of  the  body,  through  which  it  makes  its  way  back  to 
the  heart.  During  this  return  journey  it  is  usually  made 
to  traverse  definite  respiratory  organs,  either  situated  upon 
the  legs  or,  as  feathery  outgrowths,  upon  the  sides  of  the 
body,  and  generally  concealed  under  the  carapace.  A  por- 
tion of  the  blood  is  also  continually  sent  to  the  kidneys, 
which  are  located  either  at  the  base  of  the  second  antenna? 


108  ANIMAL  FORMS 

(and  known  as  green  glands),  as  in  the  crayfishes  or  crabs, 
or  on  the  second   maxillae  (shell-glands)  in  many  of  the 


FIG.  65.— Dissection  of  crayfish,    b,  brain  ;  h,  heart ;  i,  intestine  ;  k,  kidney  ;  /,  liver  ; 
n,  nerve-cord  ;  r,  reproductive  organ  ;  s,  stomach,  showing  two  teeth  in  position. 

simpler  crustaceans.  Their  method  of  operation  is  much 
like  that  of  the  kidneys  in  the  earthworm. 

107.  Nervous  system  and  special  senses. — The  nervous  sys- 
tem also  shows  a  decided  resemblance  to  that  of  the  anne- 
lids. The  cerebral  ganglia  or  brain  is  situated  above  the 
alimentary  canal  in  the  head,  and  connects  with  the  ven- 
trally  lying  cord  by  a  collar.  As  in  the  earthworm,  this 
ventral  cord  is  double,  and  bears  a  pair  of  swellings  or  gan- 
glia in  each  segment.  In  the  crayfish,  crabs,  and  other 
highly  modified  forms,  where  the  segments  tend  to  fuse, 
several  of  these  ganglia  may  also  unite,  and  except  in  early 
life  their  number  cannot  be  determined. 

Among  the  less  specialized  Crustacea  the  order  of  intel- 
ligence is  low,  though  perhaps  it  may  prove  to  be  higher 
than  is  usually  supposed  when  such  forms  have  been  more 
thoroughly  studied.  The  following  quotation  relating  to 
the  lobster  applies  even  more  to  the  higher  forms,  the 
crabs  :  "  Sluggish  as  it  often  appears  when  out  of  water  and 
when  partially  exhausted,  it  is  quite  a  different  animal  when 
free  to  move  at  will  in  its  natural  environment  on  the  sea- 


ARTHROPODS.      CLASS  CRUSTACEA  109 

bottom.  It  is  very  cautious  and  cunning,  capturing  its 
prey  by  stealth,  and  with  weapons  which  it  knows  how  to 
conceal.  Lying  hidden  in  a  bunch  of  seaweed,  in  a  crevice 
among  the  rocks,  or  in  its  burrow  in  the  mud,  it  waits  until 
its  victim  is  within  reach  of  its  claws,  before  striking  the 
fatal  blow.  The  senses  of  sight  and  hearing  are  probably 
far  from  acute,  but  it  possesses  a  keen  sense  of  touch  and 
of  smell,  and  probably  also  a  sense  of  taste." 

Although  enclosed  in  a  horny  and  often  very  thick  and 
strong  armor,  the  sense  of  touch  is  very  keen  in  the 
Crustacea  and  in  arthropods  generally.  On  many  of  the 
more  exposed  portions  delicate  hairs  or  pits  connected 
with  the  nervous  system  occur  in  great  abundance.  Some 
of  these,  usually  on  the  antennae,  undoubtedly  serve  in 
detecting  odors,  but  the  remainder  are  considered  to  be 
tactile.  In  the  higher  Crustacea,  such  as  the  crayfish, 
lobsters,  and  crabs,  ears  are  usually  found,  consisting  of 
sacs  lined  with  similar  delicate  hairs,  and  containing  sev- 
eral minute  grains  of  sand,  which  in  many  cases  make  their 
way  through  the  small  external  opening.  Vibrations  com- 
ing through  the  water  gently  shake  the  grains  of  sand, 
causing  them  to  strike  against  the  hairs  which  communi- 
cate with  the  nervous  system— a  very  simple  ear,  yet  suffi- 
cient for  the  needs  of  the  animals. 

The  eyes  of  the  Crustacea  and  arthropods  in  general  are 
either  simple  or  compound.  The  simple  and  frequently 
single  eyes  usually  consist  of  a  relatively  few  cells  embedded 
in  a  quantity  of  pigment  and  connected  with  the  nervous 
system.  It  is  doubtful  whether  they  perceive  objects  as 
anything  more  than  highly  blurred  images,  and  perhaps 
they  merely  recognize  the  difference  between  light  and 
darkness.  The  compound  eyes,  on  the  other  hand,  are 
remarkably  complex  structures,  often  borne  on  the  tops  of 
movable  stalks,  as  in  the  common  crabs  and  crayfishes. 
Each  consists  of  an  external  transparent  cornea,  divided 
into  numerous  minute  hexagonal  areas  corresponding  to  as 


110  ANIMAL   FORMS 

many  internal  rods  of  cells,  provided  with  an  abundant 
nerve-supply.  These  latter  elements  may  perhaps  repre- 
sent simple  eyes  grouped  together  to  form  the  compound 
one ;  and  it  appears  possible  that  each  element  may  form 
a  complete  image  of  an  object,  as  each  of  our  eyes  is  known 
to  do.  On  the  other  hand,  many  hold  that  the  complete 
eye  forms  only  one  image,  a  mosaic,  each  element  con- 
tributing its  share. 

108.  Growth  and  development. — As  we  have  seen,  the 
simpler  Crustacea  hatch  as  minute  larvae  (Fig.  56),  and  dur- 
ing their  growth  to  the  adult  condition  are  especially  sub- 
ject to  the  attacks  of  multitudes  of  hungry  enemies.  In 
the  higher  forms,  such  as  the  crabs,  some  of  these  early 
transformations  take  place  while  the  young  are  still  within 
the  egg  and  attached  to  the  parent.  Accordingly,  the  little 
ones  are  fairly  similar  to  their  parents,  and  their  later  his- 
tory is  very  well  exemplified  by  the  lobster. 

The  eggs  of  the  lobster  are  most  frequently  hatched  in 
the  summer  months,  usually  July,  after  they  have  been 
carried  by  the  parent  for  upward  of  a  year.  The  young, 
about  a  third  of  an  inch  in  length,  at  once  disperse,  undergo 
four  or  five  moults  during  the  next  month,  then,  ceasing 
their  swimming  habits,  settle  to  the  bottom  among  the 
rocks.  At  this  time,  twice  their  original  size,  they  closely 
resemble  their  parents,  and  their  further  development  is 
largely  an  increase  in  size.  "  The  growth  of  the  lobster, 
and  of  every  arthropod,  apparently  takes  place,  from  in- 
fancy to  old  age,  by  a  series  of  stages  characterized  by  the 
growth  of  a  new  shell  under  the  old,  by  the  shedding  of 
the  outgrown  old  shell,  a  sudden  increase  in  size,  and  the 
gradual  hardening  of  the  shell  newly  formed,  ^ot  only  is 
the  external  skeleton  cast  off  in  the  moult  and  the  linings 
of  the  masticatory  stomach,  the  esophagus,  and  intestine, 
but  also  the  internal  skeleton,  which  consists  for  the  most 
part  of  a  complicated  linkwork  of  hard  tendons  to  which 
muscles  are  attached.'? 


ARTHROPODS.      CLASS  CRUSTACEA 


111 


109.  Peripatus  (class  Onychophora).—  It  is  generally  be- 
lieved that  the  Crustacea,  insects,  and  spiders,  together 
with  their  numerous  relatives,  trace  their  ancestry  back  to 
animals  that  bore  a  certain  resemblance  to  the  segmented 
worms.     Most  of  these  ancient  types  have 

long  been  extinct,  but  here  and  there 
throughout  the  earth  we  occasionally  meet 
with  them. 

Among  the  most  interesting  of  these 
are  a  few  widely  distributed  species  belong- 
ing to  the  genus  Peripatus  (Fig.  66),  but  as 
they  are  comparatively  rare  we  shall  dis- 
miss them  with  a  very  brief  description. 
They  usually  dwell  in  warm  countries,  un- 
der rocks  and  decaying  wood,  emerging  at 
night  to  feed  on  insects,  which  they  ensnare 
in  the  slime  thrown  out  from  the  under 
surface  of  the  head.  Their  external  form, 
their  excretory  system,  and  various  other 
organs  are  worm-like.  On  the  other  hand, 
the  appendages  are  jointed,  and  one  pair 
has  been  modified  into  jaws.  The  peculiar 
breathing  organs  characteristic  of  the  in- 
sects are  also  present.  Peripatus  therefore 
gives  us  an  interesting  link  between  the 
worms  and  insects,  and  also  affords  an  idea 
of  the  primitive  insects  from  which  the 
modern  forms  have  descended. 

110.  The  centipeds  and  millipeds  (class 
Myriapoda). — Many  of  the  myriapods — that 
is,  the  centipeds  and  thousand-legged  worms 
— are  familiar  objects  under  logs  and  stones 
throughout  the  United  States.     The  first  of  these  (Fig.  67) 
are  active,  savage  creatures,  devouring  numbers  of  small 
animals,  which  they  sting  by  means  of  poison-spines  on  the 
tips  of  the  first  pair  of  legs.    The  bite  of  the  larger  tropical 


FIG.  66.— Peripatns 
(Peripatus  eiseni). 
Twice  the  natural 


112  ANIMAL   FORMS 

species  especially  causes  painful  but  not  fatal  wounds  in 
man. 

On  the  other  hand,  the  millipeds  (Fig.  68)  or  thousand- 
legs  are  cylindrical,  slow-going  animals,  feeding  on  vegetable 


PIG.  67.— Centiped. 
One-half  natural  size. 


FIG.  68.— Thousand-legs  or  milliped  (Julus). 
Natural  size. 


substances  without  causing  any  particular  damage,  except  in 
the  case  of  the  "  cutworms,"  which  often  work  great  injury 
to  crops.  When  disturbed  they  make  little  effort  to  escape, 
but  roll  into  a  coil  and  emit  an  offensive-smelling  fluid, 
which  renders  them  unpalatable  to  their  enemies. 

All  present  a  great  resemblance  to  the  segmented  worms, 
as  their  popular  names  often  testify ;  but,  on  the  other 
hand,  many  points  in  their  organization  indicate  a  closer 
relationship  to  the  insects.  As  in  the  latter,  the  head  is 
distinct,  and  bears  a  pair  of  antennae,  the  eyes,  and  two  or 
three  pairs  of  mouth-parts.  The  trunk  is  more  worm-like, 
and  consists  of  a  number  of  similar  segments,  each  bearing 


ARTHROPODS.      CLASS  CRUSTACEA  113 

one  or  two  pairs  of  jointed  legs.  In  their  internal  organ- 
ization the  character  of  the  various  systems  closely  resem- 
bles that  of  the  insects,  and  will  be  more  conveniently 
described  in  that  connection. 

Among  the  myriapods  the  females  are  usually  larger 
than  the  males.  Some  of  the  centipeds  deposit  a  little 
mass  of  eggs  in  cavities  in  the  earth  and  then  abandon 
them,  while  others  wrap  their  bodies  about  them  and  pro- 
tect them  until  the  young  are  hatched.  The  millipeds  lay 
in  the  same  situations,  but  usually  plaster  each  egg  over 
with  a  protective  layer  of  mud.  After  several  weeks  the 
young  appear,  often  like  their  parents  in  miniature,  but  in 
other  species  quite  unlike,  and  requiring  several  molts  to 
complete  the  resemblance. 


CHAPTER  X 

ARTHROPODS  (Continued}.    CLASS  INSECTS 

111.  Their  numbers. — It  has  been  estimated  that  upward 
of  three  hundred  thousand  named  species  of  insects  are 
known  to  the  zoologist,  and  that  these  represent  a  fifth,  or 
possibly  a  tenth,  of  those  living  throughout  the  world.   Many 
of  these  species,  as  the  may-flies  and  locusts,  are  represented 
by  millions  of  individuals,  which  sometimes  travel  in  such 
great  swarms  that  they  darken  the  sky.     With  nearly  all 
of  these  the  struggle  for  existence  is  fierce  and  unrelenting, 
and   it   is   little  wonder   that   such   plastic   animals  have 
changed  in  past  times  and  are  now  becoming  modified  in 
order  to  adapt  themselves  to  new  situations  where  food  is 
more  abundant  and  the  conditions  less  severe.     Owing  to 
such  modifications  we  find  some  species  fitted  for  flyiug, 
others  for  running  and  leaping,  or  for  a  life  underground, 
and  many  for  a  part  or  all  of  their  lives  are  aquatic  in  their 
habits. 

112.  External   features. — The   body  of  an   insect— the 
grasshopper,  for  example — consists  of  a  number  of  rings 
arranged  end  to  end,  as  we  have  seen  them  in  the  Crustacea 
and   the   segmented  worms.      In  the  abdomen  these  are 
clearly  distinct,  but  in  the  thorax,  and  especially  the  head, 
they  have  become  so  intimately  united  that  their  number 
is  a  matter  of  uncertainty.      These  three  regions — head, 
thorax,  and  abdomen — are  usually  clearly  defined  in  most 
insects,  but  they  are  modified  in  innumerable  ways  in  ac- 
cordance with  the  animal's  mode  of  life. 

114 


ARTHROPODS.    CLASS  INSECTS  115 

The  head  usually  carries  the  eyes,  a  pair  of  feelers  (an- 
tennae), and  three  pairs  of  mouth-parts  which  may  be  fash- 
ioned into  a  long,  slender  tube  to  be  used  in  sucking,  and 
frequently  as  a  piercing  organ  ;  or  they  may  be  constructed 
for  cutting  and  biting.  The  thorax  bears  three  pairs  of 
legs  and  often  one  or  two  pairs  of  wings.  The  appendages 
of  the  abdomen  are  usually  small  and  few  in  number,  or 
even  absent. 

113.  Internal  anatomy.— The  restless  activity  of  insects 
is  proverbial.  Some  appear  to  be  incessantly  moving  about, 
either  on  the  wing  or  afoot,  and  are  endowed  with  com- 
paratively great  strength.  Ants  and  beetles  lift  many  times 
their  own  weight.  Numerous  insects  are  able  to  leap  many 
times  their  own  length,  and  others  perform  different  kinds 
of  work  with  a  vigor  and  rapidity  unsurpassed  by  any  other 
class  of  animals.  As  is  to  be  expected,  the  muscular  sys- 
tem is  well  developed,  and  exhibits  a  surprising  degree  of 
complexity.  Over  five  hundred  muscles  are  required  for 
the  various  movements  of  our  own  bodies,  but  in  some  of 
the  insects  more  than  seven  times  this  number  exist.  The 
amount  of  food  necessary  to  supply  this  relatively  immense 
system  with  the  required  nourishment  is  correspondingly 
large.  Many  insects,  especially  in  an  immature  or  larval 
condition,  devour  several  times  their  own  weight  each  day. 
Their  food  may  consist  of  the  juices  of  animals  or  plants, 
which  they  suck  out,  or  of  the  firmer  tissues,  which  are 
bitten  or  gnawed  off. 

Xot  only  do  the  mouth-parts  stand  in  direct  relation  to 
the  habits  of  the  animal  and  to  its  food,  but,  as  we  have 
often  noticed  before,  the  internal  organization  is  also 
adapted  for  the  digestion  and  distribution  of  the  nutritive 
substances  in  the  most  economical  way.  For  this  reason 
we  find  the  alimentary  canal  differing  widely  in  the  various 
forms  of  insects.  In  each  case  it  extends  from  the  mouth 
to  the  opposite  end  of  the  animal,  and  ordinarily  consists 
of  a  number  of  different  parts.  In  the  insect  shown  in 


116 


ANIMAL  FORMS 


Fig.  69  the  mouth  soon  leads  into  the  esophagus,  which 
in  turn  leads  into  the  crop  that  serves  to  store  up  the  food 
until  ready  for  its  entry  into  the  stomach ;  or  in  some  of 
the  ants,  bees,  and  wasps  it  may  contain  material  which 

may  be  disgorged  and  fed 
to  the  young.  In  many 
cases  the  stomach  is  small 
and  ill-defined  as  in  Fig.  69, 
and  again  it  may  reach 
enormous  dimensions,  near- 
ly filling  the  body.  It  may 
also  bear  numerous  lobes  or 
delicate  hair-like  processes, 
which  afford  a  greater  sur- 
face for  the  absorption  of 
food.  Behind  the  stomach 
are  a  number  of  slender 
outgrowths  that  are  believed 
to  act  as  kidneys.  Beyond 
their  insertion  lies  the  in- 
testine, which,  like  the 
stomach,  is  the  subject  of 
many  modifications  in  the 
different  kinds  of  insects. 

The  digested  food  is  rap- 
idly absorbed  through  the  coats  of  the  stomach  and  intes- 
tine and  enters  a  circulatory  system  which  reminds  us  of 
what  exists  in  many  of  the  Crustacea.  The  heart  is  situ- 
ated above  the  digestive  tract,  and  from  it  arteries  pass  out 
to  different  parts  of  the  body.  Here  the  blood  leaves  the 
vessels  and  is  poured  directly  into  the  spaces  among  the 
viscera,  whence  it  is  finally  conducted  through  irregular 
channels  to  the  heart  by  its  pulsations. 

In  the  Crustacea  the  blood  is  made  to  pass  through  a 
respiratory  system  usually  in  the  form  of  definite  gills,  and 
the  oxygen  with  which  it  is  charged  is  distributed  to  all 


FIG.  69.— Cockroach,  dissected  to  show  ali- 
mentary canal,  al.  c.— After  HATSELEK 
and  CORI. 


ARTHROPODS.     CLASS   INSECTS  117 

parts  of  the  body.  In  the  insects  the  blood  serves  almost 
entirely  to  carry  the  food,  and  the  oxygen  is  conveyed 
through  the  animal  by  a  remarkable  contrivance  found 
only  in  the  insects,  the  spiders,  and  a  few  related  forms. 

114.  Respiratory  system. — If  we  examine  an  insect,  the 
grasshopper  for  example,  we  find  a  number  of  small  brown 
spots  on  each  side  of  the  abdomen,  each  of  which  under  a 
magnifying-glass  is  seen  to  be  perforated  by  a  narrow  slit. 
Carefully  opening  the  body,  we  find  that  each  slit  is  in 
communication  with  a  white,  glistening  tube  that  rapidly 
branches  and  penetrates  to  all  parts  of  the  animal.     When 
the  body  is  expanded  the  air  rushes  into  the  outer  openings, 
on  through  the  open  tubes,  and  is  distributed  with  great 
rapidity  to  all  the  tissues  of  the  body.     In  many  insects 
some  of  these  tubes  connect  with  air-sacs  which  probably 
serve   to  buoy  up  the   insect   during  its  flights   through 
the  air. 

115.  Wingless  insects  (Thysanura). — The  simplest  of  all 
insects  are  the  fishmoths  and  springtails,  relatively  small 
organisms  covered  with  shining  scales  or  hairs.     The  first 
of  these  is  occasionally  seen  running  about  in  houses  feed- 
ing upon  cloth  and  other  substances,  while  the  latter  live 
in  damp  places  under  stones  and  logs.     They  are  without 
wings,  but  are  able  to  run  rapidly  and  to  leap  considerable 
distances.     In  addition  to  the  ordinary  appendages,  the 
abdomen  bears  what  are  perhaps  rudimentary  legs,  a  fact 
which,    together   with   their   relatively   simple   structure, 
strengthens  the  belief  that   the  insects  have   descended 
from  centiped-like  ancestors. 

116.  Grasshoppers,  crickets,  katydids,  etc.  (Orthoptera). — 
Rising  higher  in  the  scale  of  insect  life,  we  arrive  at  the  group 
of  the   cockroaches,    crickets,   grasshoppers,   locusts,  and 
other  related  insects.     Four  wings  are  present,  the  first  pair 
thickened  and  overlapping  the^  second  thinner  pair.     The 
latter  are  folded  lengthwise  like  a  fan,  which  is  said  to  have 
given  the  name  Orthoptera  (meaning  straight-winged)  to 


118  ANIMAL  FORMS 

this  group  of  insects.  These  extend  all  over  the  world, 
being  particularly  abundant  in  the  warmer  countries,  and 
their  strong  biting  mouth-parts  and  voracious  appetites 
render  many  of  them  dreaded  pests  to  the  farmer.  The 
cockroaches  are  nocturnal  in  their  habits,  racing  about  at 
night,  devouring  victuals  in  the  pantry  and  gnawing  the 
bindings  of  books.  During  the  day  their  flat  bodies  enable 
them  to  secrete  themselves  in  crevices  wherever  there  is 
sufficient  moisture. 

In  the  grasshoppers,  locusts,  katydids,  and  crickets  the 
body  is  more  cylindrical,  and  the  hind  pair  of  legs  are  often 
greatly  lengthened  for  leaping.  The  crickets  and  katydids 
are  nocturnal,  the  former  re- 
maining by  day  in  burrows 
which  they  construct  in  the 
earth,  the  latter  resting  qui- 
etly in  the  trees.  At  night 

FIG.  70.— The  Rocky  Mountain  locust.—          .    *        , 

After  RILEY,  from  The  insect  World.  they  f  east  upon  vegetable 
matter  principally,  though 

some  species  are  known  to  prey  on  small  animals.  Those 
insects  we  usually  term  grasshoppers  (properly  called  lo- 
custs) are  specially  destructive  to  vegetation.  Some  spe- 
cies are  strong  fliers,  and  this,  connected  with  their  abil- 
ity to  multiply  rapidly,  renders  them  greatly  dreaded  pests. 
They  have  been  described  as  flying  in  great  swarms/form- 
ing  black  clouds,  even  hiding  the  sun  as  far  as  the  eye 
could  reach.  The  noise  made  by  their  wings  resembled 
the  roar  of  a  torrent,  and  when  they  settled  upon  the  earth 
every  vestige  of  leaf  and  delicate  twig  soon  disappeared. 

The  eggs  of  the  majority  of  Orthoptera  are  laid  in  the 
ground,  where  they  frequently  remain  through  the  winter. 
When  hatched  the  young  quite  closely  resemble  the  parents, 
and,  after  a  relatively  slight  metamorphosis,  assume  the 
adult  form. 

117.  Dragon-flies,  may-flies,  white  ants,  etc.  (Neuroptera).— 
The  dragon-,  caddis-,  may-flies,  ant  lions,  and  the  white  ants 


ARTHROPODS.    CLASS  INSECTS 


119 


possess  four  thin  and  membranous  wings  incapable  of  being 
folded.  These  possess  a  network  of  delicate  nervures,  giv- 
ing the  name  Neuroptera  (meaning  nerve-winged)  to  the 
class.  Of  the  forms  mentioned  above,  all  but  the  white 
ants  lay  their  eggs  in  the  water,  and  the  developing  larvae 


FIG.  71.— Dragou-fly  (LibeUula  pulchella). 


spend  their  lives  in  this  medium  until  the  time  comes  for  their 
complete  metamorphosis  into  the  adult.  The  larvae  of  the 
caddis-flies  protect  themselves  within  a  tube  of  stones  or  sticks 
bound  together  with  silken  threads,  which  they  usually 
attach  to  the  under  side  of  stones  in  running  water.  On 
the  other  hand,  the  young  of  the  dragon-  and  may-flies,  pro- 
vided with  strong  jaws,  are  active  in  the  search  of  food  and 
very  voracious.  In  time  they  emerge  from  their  larval  skin 
and  the  water  in  which  they  live,  and  after  a  life  spent  on 
the  wing  they  deposit  their  eggs  and  perish.  The  adult 
ant-lion,  which  has  somewhat  the  appearance  of  a  small 
dragon-fly,  lays  its  eggs  in  light  sandy  soil.  In  this  the 
resulting  larvae  excavate  funnel-shaped  pits,  at  the  bottom 
of  which  they  lie  concealed.  Insects  stumbling  into  their 
9 


120 


ANIMAL  FORMS 


pitfalls  are  pelted  with  sand,  which  the  ant-lion  throws  at 
them  with  a  jerky  motion  of  the  head,  and  are  speedily 
tumbled  down  the  shifting  sides  of  the  funnel  to  be  seized 
and  devoured. 

While  the  white  ants  are  not  in  any  way  related  to  the 
true  ants,  they  possess  many  similar  habits.  Associated  in 
great  companies,  they  excavate  winding  galleries  in  old  logs 
and  stumps,  and,  further,  are  most  interesting  because  of 
the  division  of  labor  among  the  various  members.  The 
wingless  forms  are  divided  into  the  workers,  which  exca- 
vate, care  for  the  young,  and  otherwise  labor  for  the  good 
of  the  others ;  and  into  the  soldiers,  huge-headed  forms. 


Fiu.  72.— Ant-lion  larva  plowing  its  way  through  the  sand  (upper  figure)  while  an- 
other is  commencing  the  excavation  of  a  funnel-shaped  pit  similar  to  one  on  right. 


Photograph  by  A.  L.  MEL&NDER  and  C.  T.  BRCES. 


whose  strong  jaws  serve  to  protect  the  colony.  The  re- 
maining winged  forms  are  the  kings  and  queens.  In  the 
spring  many  of  the  royalty  fly  away  from  home,  shed  their 
wings,  unite  in  pairs,  and  set  about  to  organize  a  colony. 
The  queen  rapidly  commences  to  develop  eggs,  and  in  some 


ARTHROPODS.    CLASS  INSECTS 


121 


species  her  body  becomes  so  enormously  distended  with 
these  that  she  loses  the  power  of  locomotion  and  requires 
to  be  fed.  A  single  queen  has  been  known  to  lay  eggs  at 
the  rate  of  sixty  per  minute  (eighty  thousand  a  day),  and 


FIG.  73. — Termites  or  white  ants,     a,  queen  ;  b,  winged  male  ;  c,  worker;  d,  soldier. 

those  destined  to  royal  rank  are  so  nursed  that  they  advance 
farther  in  their  development  than  the  remaining  sterile 
and  wingless  forms. 

118.  The  bugs  (Hemiptera).— .The  large  and  varied  group 
of  the  bugs  (Hemiptera)  includes  a  number  of  semi-aquatic 
species,  such  as  the  water-boatmen,  often  seen  rowing 
themselves  along  in  the  ponds  by  means  of  a  pair  of  oar- 
shaped  legs,  in  search  of  other  insects.  Somewhat  similar 
at  first  sight  are  the  back-swimmers,  with  like  rowing 
habits,  but  unique  in  swimming  back  downward.  Both  of 
these  bugs  frequently  float  at  the  surface,  and  when  about 
to  undertake  a  subaquatic  journey  they  may  be  seen  to 
imprison  a  bubble  of  air  to  take  along.  Closely  related  are 
the  giant  water-bugs  (Fig.  74),  which  often  fly  from  pond 
to  pond  at  night.  In  such  flights  they  are  frequently 


122 


ANIMAL  FORMS 


attracted  by  lights,  and  have  come  to  be  called  "  electric- 

light  bugs." 

Among  our  most  dreaded  insect  pests  are  the  chinch- 

bugs  —  small  black-and-white  insects,  but  traveling  in  com- 
panies aggregating  many  millions. 
As  they  go  they  feed  upon  the 
stems  and  leaves  of  grain,  which 
they  devour  with  extraordinary  ra- 
pidity. The  squash-bug  family  is 
also  extensive,  and  destructive  to 
the  young  squash  and  pumpkin 
plants  in  the  early  spring. 

The  lice  are  small,  curiously 
shaped  bugs,  which  suck  the  blood 
of  other  animals.  The  plant-lice, 
also  small,  suck  the  juices  of 
plants,  and  are  often  exceedingly 
destructive.  This  is  especially  true 
of  the  phylloxera,  a  plant-louse 

hj   h    caugeg   ammally  the  loss   Qf 
.1 

millions  of  dollars  among  the  vine- 
yards of  this  and  other  countries. 

Even  more  destructive  are  tha  scale-insects,  curiously  mod- 
ified forms,  of  which  the  wingless  females  may  be  found  on 
almost  any  fruit-tree  and  on  the  plants  in  conservatories, 
their  bodies  covered  with  a  downy,  waxy,  or  other  kind  of 
covering,  beneath  which  they  remain  and  lay  their  eggs. 

119.  The  flies  (Diptera).  —  The  group  of  the  Diptera 
(meaning  two-winged)  includes  the  gnats,  mosquitoes,  fleas, 
house-flies,  horse-flies  (Fig.  75),  and  a  vast  company  of 
related  forms.  Only  a  single  pair  of  wings  is  present,  the 
second  pair  being  rudimentary  or  fashioned  into  short, 
thread-like  appendages  known  as  balancers,  though  they 
probably  act  as  sensory  organs  and  are  not  directly  con- 
cerned with  flight.  The  mouth-parts  are  adapted  for  pier- 
cing and  sucking.  The  eyes,  constructed  on  the  same  plan 


FIG.    '-l.-Giant  water-bug 

phus  dtlalatus),  with  eggs  at- 

tached. 


ARTHROPODS.    CLASS  INSECTS 


123 


FIG.  75.— Horse-fly  ( Therio- 
plectes). 


as  those  of  the  Crustacea,  are  comparatively  large,  and  are 
frequently  composed  of  a  great  number  of  simple  eyes 
united  together,  upward  of  four 
thousand  forming  the  eye  of  the 
common  house-fly. 

These  insects  are  widely  distrib- 
uted throughout  the  world,  where 
they  inhabit  woods,  fields,  or  houses 
as  best  suits  their  needs.  Their 
food  is  varied.  Some  suck  the 
juices  of  plants,  others  attack  ani- 
mals, and,  while  many  are  trouble- 
some pests,  others,  especially  in  the 
early  stages  of  their  existence,  are 
of  great  benefit. 

120.  Familiar  examples.— Owing 
to  the  widely  different  habits  and 
structure  of  the  members  of  this  group,  we  shall  briefly 
consider  two  examples,  the  mosquito  and  the  house-fly, 
which  will  give  us  a  fairly  good  idea  of  the  characteristics 
of  all.  The  eggs  of  the  mosquito  are  laid  in  sooty-look- 
ing masses  on  the  surface  of  stagnant  pools.  Within  a 
very  short  time  the  young  hatch,  and,  owing  to  their  pecul- 
iar swimming  movements, are  known  as  "wrigglers."  They 
are  then  active  scavengers,  devouring  vast  quantities  of 
noxious  substances  and  performing  a  valued  service.  They 
frequently  rise  to  the  surface,  take  air  into  the  tracheal 
system,  which  opens  at  the  posterior  end  of  the  body,  and 
descend  again.  After  an  increase  in  growth  and  many  in- 
ternal changes  resulting  in  a  chrysalis-like  stage,  they  rise 
to  the  surface,  split  the  shell,  and,  using  the  latter  as  a  float, 
carefully  balance  themselves  and  soon  fly  away. 

The  house-fly  usually  lays  its  eggs  in  decaying  vegetable 
matter,  and  the  young,  maggot-like  in  form,  are  active 
scavengers.  They  too  undergo  deep-seated  changes  during 
the  next  few  days,  finally  transforming  into  the  adult. 


124 


ANIMAL   FORMS 


Many  of  this  great  group  of  the  flies  spend  their  early  life 
in  the  water  or  other  medium  acting  as  scavengers ;  but,  on 
the  other  hand,  numbers  attack  domestic  and  other  animals, 
and  throughout  their  entire  lives  are  an  intolerable  plague. 
121.  The  beetles  (Coleoptera).— Owing  to  the  ease  of  pres- 
ervation and  their  bright  colors,  the  beetles  have  probably 
been  more  widely  collected  than  other  insects.  Fully  ten 


**^T 

FIG.  76.— Long-honied  borer  (Ergates).     Larva  (left-hand  figure),  pupa,  and  adult 


thousand  distinct  species  are  known  in  Xorth  America 
alone.  They  are  all  readily  recognized  by  the  two  firm, 
horny  sheaths  enclosing  the  two  membranous  wings,  which 
alone  are  organs  of  flight.  The  mouth  is  provided  with 
jaws,  which  are  used  in  gnawing.  Some  prey  on  noxious 
insects  or  upon  decaying  vegetable  or  animal  matter,  and 
are  often  highly  beneficial ;  but  others  attack  our  trees  and 
domestic  animals,  and  work  incalculable  damage. 


ARTHROPODS.    CLASS  INSECTS  125 

In  some  of  the  stag-  or  wood-beetles  (Fig.  76),  which 
we  may  select  as  types,  the  adults  are  often  found  crawling 
about  on  or  beneath  the  bark  of  trees,  living  on  sap  or 
small  animals.  The  eggs  laid  in  these  situations  develop 
into  grub-like  larvae,  which  bore  their  way  through  living 
or  dead  wood,  and  in  this  condition  sometimes  live  four  or 
five  years.  They  then  transform  into  quiescent  pupae  (Fig. 
76),  which  finally  burst  their  shells  and  emerge  in  the 
adult  form.  Others,  like  water-beetles  and  the  whirligig- 
beetles,  whose  mazy  motions  are  often  seen  on  the  surface 
of  quiet  streams,  pass  the  larval  period  in  the  water. 
Under  somewhat  different  conditions  we  find  the  potato- 
bugs,  lady-bugs,  fire-flies,  and  their  innumerable  relatives, 
but  the  changes  they  undergo  in  becoming  adult  are  essen- 
tially the  same  as  those  described  for  the  other  members  of 
the  order. 

122.  The  moths  and  butterflies  (Lepidoptera). — The  moths 
and  butterflies  occur  all  over  the  world.  In  their  mature 


FIG.  77.— Monarch-butterfly  (Anoaia  i>lezipi)i/ti>.     From  photograph  by  A.  L.  MELAN- 
DER  and  C.  T.  BRUES. 

state  they  are  possessed  of  a  grace  of  form  and  movement 
and  a  brilliancy  of  coloration  that  elicit  our  highest  admi- 
ration. The  mouth-parts  are  developed  into  a  long  pro- 
boscis, which  may  be  unrolled  and  used  to  suck  the  nectar 
out  of  flowers,  though  in  many  of  the  adult  moths,  which 
never  feed,  it  may  remain  unused.  The  wings,  four  in 
number,  are  covered  with  beautiful  overlapping  scales  that 


126 


AN7IMAL   FORMS 


adhere  to  our  fingers  when  handled.     This  feature,  and 
the  general  plan  of  the  body,  which  is  much  the 


FIG.  78.— The  silver-spot  (Argyituis  cybele).    Photograph  by  A.  L.  MELANDEK  and 
C.  T.  BRI-ES. 

throughout   the  group,  enables  us   to  recognize  most  of 
them  at  once. 

123.  Development  and  metamorphosis. — In  some  of  the 
simplest  insects,  as  in  the  bugs,  the  young  at  birth  resemble 
their  parents.  In  other  insects  the  resemblance  is  not  so 
close.  The  young  grasshopper,  for  example,  hatches,  from 
an  egg  laid  in  the  ground,  with  a  ridiculously  large  head 
and  staring  eyes ;  still  there  is  no  difficulty  in  recognizing 
its  relationships.  During  the  next  week  internal  changes 
take  place.  The  shell  is  burst,  and  the  grasshopper  emerges, 
looking  more  like  its  parents  than  before.  This  process  is 
repeated  four  or  five  times  during  the  next  few  weeks,  and 
the  gradual  changes  thus  produced  finally  bring  the  young 
insect  to  the  adult  form.  This  latter  state  has  been  attained 
by  an  incomplete  metamorphosis. 


ARTHROPODS.     CLASS   INSECTS 


127 


In  the  flies,  beetles,  butterflies,  and  numerous  insects 
the  differences  between  the  newly  hatched  young  and  the 
adult  are  vastly  greater.  No  one  looking  on  a  caterpillar 
or  a  grub  for  the  first  time  would  suspect  its  origin,  and 
the  changes  they  undergo  have  attracted  attention  for  cen- 
turies. Placing  any  of  the  ordinary  caterpillars  with  their 
favorite  food  in  a  glass-covered  box,  we  may  readily  watch 
their  transformations.  Provided  with  biting  mouth-parts 
and  a  voracious  appetite,  they  devour  vast  quantities  of 
vegetation  for  several  days.  Finally  they  cease  eating,  and 


FIG.  79.— Life:history  of  silk-moth  (Bombyx  mori).    A,  adult ;  B,  C.  D,  caterpillars  of 
different  ages  ;  E,  F,  G,  silken  cocoon  and  pupa  ;  H,  eggs. 

suspend  themselves  head  downward  by  means  of  a  kind  of 
cobweb.  After  remaining  quiet  a  few  hours,  they  burst 
their  skin,  and  within  appears  a  chrysalis  or  pupa.  In  the 
moths,  for  example,  the  silk-moth  (Fig.  79),  the  caterpillar 
or  silk-worm,  after  eating  the  favorite  mulberry  leaves, 
spins  a  silken  cocoon,  in  which  the  pupa  is  produced.  The 
larvae  of  beetles  and  many  other  insects  excavate  tunnels  in 
wood  or  in  the  earth,  and  there  undergo  their  transforma- 
tions. Invariably  the  pupa  remains  quiet  for  days,  months, 


128  ANIMAL   FORMS 

or  even  years,  but  when  the  proper  time  arrives  the  fully 
formed  insect  emerges,  and  takes  to  the  wing. 

Wonderful  internal  changes  have  been  taking  place 
during  this  time.  The  organs  fitted  for  the  proper  treat- 
ment of  the  vegetable  food  of  the  caterpillar  or  grub  are 
destroyed,  at  least  in  part,  and  new  systems  are  produced 
ready  for  the  nectar  and  vegetable  juices  which  are  to  be 
the  food  of  the  adult  insect.  All  insects  that  pass  through 
a  pupal  quiescent  stage  are  said  to  undergo  a  complete 
metamorphosis. 

124.  The  ants,  bees,  wasps,  etc.  (Hymenoptera). — The  ants, 
bees,  and  wasps  are  the  best-known  insects  belonging  to 
this  order.     They  are  characterized  by  four  membranous 
wings,  by  biting  and  sucking  mouth-parts,  and  the  female 
is  often  provided  with  a  sting.     All  undergo  a  complete 
metamorphosis.     The  eggs  may  be  laid  in  the  bodies  of 
other  insects,  many  of  which  are  pests,  and  are  thus  de- 
stroyed ;  or  they  may  be  deposited  in  the  nests  of  other 
insects,  the  foster-parents  being  compelled  to  feed  them ; 
or  they  may  be  placed  in  marvelously  constructed  homes, 
and  be  the  objects  of  the  greatest  attention,  the  parents  or 
attendants   often   risking   or  losing    their   lives    in   their 
defense.     The  members  of  this  order  have  long  attracted 
attention,  largely  on  account  of  their  remarkable  instinc- 
tive powers.     They  live  in  highly  organized  communities 
and  certain  of  their  characteristics  may  be  illustrated  by 
a  study  of  some  of  the  more  familiar  forms. 

125.  The  ants. — The  ants  live  in  communities  consisting 
of  anywhere  from  a  dozen  to  many  thousands  of  individuals, 
according  to  the  species.      Each  of  these  colonies  contains 
the  queen,  several  young  winged  males  and  females,  des- 
tined as  kings  and  queens  to  found  new  colonies,  and  of  a 
far  greater  number  of  wingless  sterile  females,  the  workers. 
The  workers  construct  the  greater  part  of  the  nest,  which 
often  consists  of  extensive  galleries,  nurseries,  and  grana- 
ries, excavated  in  wood  or  in  the  earth.     They  also  attend 


ARTHROPODS.    CLASS  INSECTS  129 

to  the  acquisition  of  food,  which  consists  of  the  sweet 
juices  of  plants,  of  other  insects,  or  of  leaves  and  seeds. 
These  may  be  fed  at  once,  or  placed  in  storehouses  until 
times  of  need. 

Certain  species  of  ants  make  carefully  planned  attacks 
upon  other  weaker  forms.  The  young  are  carried  off,  at 
times  only  after  a  prolonged  and  fierce  struggle,  and  all 
are  soon  eaten,  or  a  few  may  be  allowed  to  develop  and  act 
as  slaves.  Some  species  are  unable  to  exist  without  serv- 
ants, which  feed  them,  wash  them,  and  otherwise  minister 
to  their  comfort. 

In  some  of  their  raids  numerous  plant-lice  (delicate, 
usually  green,  insects,  such  as  occur  on  our  household 
plants)  are  often  captured  and  carried  into  the  nest.  These 
so-called  "  ant-cows "  are  carefully  tended,  and  in  return 
yield  up  a  tiny  drop  of  a  sugary  fluid  to  the  hungry  ant 
that  solicits  it. 

The  eggs  laid  by  the  queen  develop  into  white  worm- 
like  creatures,  which  ordinarily  spin  cocoons  when  about  to 
become  pupae.  These  are  incorrectly  called  "ant-eggs." 
Many,  probably  on  account  of  insufficient  nourishment, 
never  develop  reproductive  organs.  They  become  the  neu- 
ters or  workers.  The  winged  royalty  fly  away  from  the 
colony,  pair  and  found  homes  of  their  own,  and  become 
surrounded  by  a  numerous  progeny. 

126.  The  bees. — Among  the  bees  we  find  a  considerable 
number  which  lead  solitary  lives,  excavating  tunnels  in 
earth  or  wood,  as  in  the  case  of  many  of  the  wasps,  but, 
unlike  them,  supplying  the  young  with  honey  or  pollen. 
Others  may  constitute  a  band  of  worthless  insects  which 
steal  their  food  from  their  more  industrious  relations,  in 
whose  nests  they  also  secretly  deposit  their  eggs,  leaving  the 
young  to  be  nourished  with  food  rightly  belonging  to  others. 

But  it  is  with  the  social  bees  we  are  most  familiar — the 
bumble-  and  honey-bees.  The  former  usually  build  in  the 
ground,  and  form  colonies  consisting  of  the  queen  and  from 


130  ANIMAL  FORMS 

twenty  to  two  hundred  workers.  Regular  combs  are  not 
constructed,  the  young  at  first  feeding  on  pollen  masses  or 
"  bee-bread,"  and  finally  spinning  cocoons.  In  the  late 
summer  males  and  females  appear,  but  as  winter  conies  on 
all  perish  except  the  queens,  which  seek  a  sheltered  place, 
and  in  the  spring  revive  to  establish  new  colonies. 

In  a  wild  state  the  honey-bees  dwell  in  cavities  of  trees 
and  other  protected  places,  where  they  form  colonies, 
consisting  of  the  queen,  of  per- 
haps two  hundred  males  or 
drones  if  the  nest  be  examined 
in  the  spring  and  summer,  and 
of  a  hundred  times  as  many 
sterile  females,  the  workers. 
These  form  among  the  most 
highly  organized  insect  soci- 
eties known.  All  work  for  the 

FIG.  80.-Bumblebee  (Bombus). 

good  of  the  colony.     To  each 

worker  is  assigned  a  definite  task,  which  is  never  shirked. 
It  must  collect  the  honey,  supply  the  wax  for  making  the 
comb,  take  care  of  the  brood,  or  in  other  ways  minister  to 
the  welfare  of  the  community.  On  the  queen  devolves 
the  entire  task  of  egg-laying.  She  may  lay  three  thousand 
eggs  a  day  and  be  fully  occupied  during  the  three  or  four 
years  that  she  lives.  The  drones,  or  males,  fertilize  most 
of  the  eggs,  and  are  then  driven  out  from  the  hive,  after 
a  stay  of  a  month  or  two.  The  eggs  unfertilized  by  the 
drones  are  placed  in  large  cells,  and  the  young  fed  on 
pollen  develop  into  males.  The  fertilized  eggs  may  pro- 
duce queens  or  workers  at  the  discretion  of  the  queen.  If 
the  latter  be  desired,  the  eggs  are  placed  in  small  cells  with 
a  scant  amount  of  food,  which  apparently  causes  the  repro- 
ductive system  to  remain  undeveloped.  The  same  eggs,  if 
placed  in  the  large  queen  cells  and  supplied  with  highly 
nutritious  food,  would  have  developed  into  queens.  When 
these  latter  appear  they  are  vigorously  attacked  and  killed 


ARTHROPODS.     CLASS  INSECTS 


131 


by  the  parent  if  not  protected  by  the  workers.  If  the 
young  queen  survive,  the  old  queen  departs  with  many  of 
her  subjects,  and  collects  them  into  a  dense  swarm  attached 
to  a  limb  of  a  tree,  where  they  remain  until  scouts  return  to 
conduct  them  to  their  new  home. 

127.  The  wasps. — The  digger-wasps  are  frequently  to  be 
seen  gnawing  tunnels  in  the  wood  or  earth,  at  the  inner  end 


FIG.  81.— Nest  of  Vespa,  a  social  wasp.    Photograph  by  A.  L.  MELANDEK  and 
C.  T.  BRUES. 

of  which  an  egg  is  laid.  In  some  species  the  developing 
young  is  nourished  by  food  carried  in  to  it  day  by  day.  In 
other  cases  the  parent  may  never  see  her  child,  dying  or 
abandoning  it  before  its  birth ;  but  before  departing  she  is 
careful  to  place  within  reach  a  sufficient  supply  of  spiders, 
caterpillars,  beetles,  or  locusts  that  shall  nourish  the  little 
one  until  it  becomes  a  motionless  pupa.  This  stage  is  soon 
over,  and  the  adult  wasp  now  digs  its  way  to  the  surface. 

Passing  by   the   familiar    mud-wasps   or  mud-daubers, 
whose  nests  are  common  objects  under  stone's  or  against 


132  ANIMAL   FORMS 

the  rafters  of  barns  and  houses,  we  arrive  at  the  social 
wasps.  As  the  name  indicates,  these  insects,  such  as  the 
yellow-jackets  and  hornets,  live  together  in  companies 
which  consist,  as  in  the  ants  and  bees,  of  males,  females, 
and  workers.  They  also  are  fond  of  the  juices  of  fruits, 
and  many  of  them  destroy  insects  which  may  be  fed  to  the 
young.  Their  nests  are  variously  situated  and  constructed, 
but  all  of  them  agree  in  being  composed,  at  least  in  part,  of 
a  grayish  substance  which  is  in  reality  a  kind  of  paper. 
With  their  jaws  they  scrape  off  from  old  logs  and  fences 
small  particles  of  wood,  which  they  probably  mix  with  saliva, 
and  rolling  the  mass  into  a  ball  set  out  for  home.  These 
pellets  are  then  flattened  out  into  thin  sheets,  and  worked 
up  into  hexagonal  cells,  in  which  the  eggs  are  laid. 

Along  with  the  nests  of  the  mud-daubers  one  frequently 
notices  the  nests  of  some  of  the  familiar  wasps  (Polistes), 
which  build  cake-like  nests  composed  of  thirty  or  forty, 
hexagonal  cells  attached  by  a  stalk.  Somewhat  similar 
nests,  though  usually  more  extensive,  are  constructed  by 
the  yellow-jackets  in  cavities  in  the  ground.  The  numer- 
ous combs  of  the  hornet  are  surrounded  by  several  sheets  of 
wood-pulp,  and  the  whole  structure  is  attached  generally 
to  the  limb  of  a  tree. 

In  the  spring  the  nests  of  all  these  species  of  wasps  are 
commenced  by  a  single  female,  who  has  lived  in  a  dormant 
condition  through  the  winter.  She  builds  a  small  nest  and 
in  time  is  surrounded  by  numerous  workers,  which  live  in 
perfect  harmony,  enlarging  the  nest  and  rearing  the  young. 
As  autumn  approaches  the  young  males  and  females  leave 
the  nest ;  but  the  males,  together  with  the  workers,  all  suc- 
cumb to  the  cold,  and  none  but  the  females  persist  to  found 
a  new  colony  the  following  spring. 


CHAPTER  XI 

ARTHROPODS  (Continued).      CLASS   ARACHNIDA 

128.  General  characters. — In  this  group,  comprising  the 
spiders,  mites,  and  a  large  assemblage  of  related  species,  we 
again  meet  with  great  differences  in  form  and  structure 
which  fit  them  for  lives  under  widely  different  conditions. 
The  three  regions  of  the  body,  head,  thorax,  and  abdomen, 
so  clearly  marked  in  the  insects,  are  here  less  plainly  de- 
fined. The  head  and  thorax  are  usually  closely  united,  and 
in  the  mites  the  boundaries  of  the  abdomen  are  also  indis- 
tinct. The  appendages  of  the  head  are  two  in  number,  and 
probably  correspond  to  the  antenna?  and  mandibles  of  other 
Arthropods.  In  the  scorpions  and  some  species  of  mites 
these  are  furnishw  with  pincers  for  holding  the  prey,  and 
in  other  forms  they  act  as  piercing  organs.  Usually  the 
thorax  bears  four  pairs  of  legs,  a  characteristic  which  readily 
separates  such  animals  from  the  insects. 

The  internal  organization  differs  almost  as  much  as  does 
the  external.  In  many  species  it  shows  a  considerable  re- 
semblance to  that  of  some  insects,  but  in  others,  especially 
those  of  parasitic  habits,  it  departs  widely  from  such  a  type. 
Eespiration  is  affected  by  means  of  tracheae,  or  lung-books, 
which  consist  of  sacs  containing  many  blood-filled,  leaf -like 
plates  placed  together  like  the  leaves  of  a  book. 

Usually,  as  in  the  insects,  the  young  hatch  from  eggs 
which  are  laid,  but  in  the  scorpions  and  some  of  the  mites 
the  young  develop  within  the  body  and  at  birth  resemble 
the  parent.  Almost  all  of  these  organisms  live  either  as 

133 


134 


ANIMAL  FORMS 


parasites  or  as  active  predaceous  animals  upon  other  animals. 
For  this  purpose  many  are  provided  with  keen  senses  for 
detecting  their  prey  and  poisonous  spines  for  despatching  it. 
129.  The  scorpions.— Owing  to  the  stout  investing  armor, 
the  strong  pincers,  and  the  general  form  of  the  body,  the 
scorpions  might  at  first  sight  be  mistaken  for  near  relatives 

of  the  crayfish  or  lobster. 
A  more  careful  examina- 
tion will  show  that  the 
two  pairs  of  pincers  prob- 
ably correspond  to  the 
antennae  and  mandibles  of 
the  Crustacea  that  have 
become  modified  for  seiz- 
ing the  food.  The  swol- 
len part  of  the  animal 
lying  behind  the  four 
pairs  of  legs  is  a  part  of 
the  abdomen,  of  which 
the  slender  "  tail "  consti- 
tutes the  remainder.  On 
the  tip  of  the  tail  is  a 
curved  spine  supplied 
with  poison  glands.  Sev- 
eral pairs  of  eyes  are  borne 
on  the  dorsal  surface  of 
the  head  and  thorax,  while 
on  the  under  side  of  the  animal  several  slit-like  openings 
lead  into  as  many  small  cavities  containing  the  lung-books. 
The  scorpions  are  the  inhabitants  of  warm  countries, 
where  they  may  be  found  under  sticks  and  stones  through- 
out the  day.  At  night  they  leave  their  homes  in  search  of 
food,  which  consists  chiefly  of  insects  and  spiders.  These 
are  seized  by  means  of  the  pincers,  and  the  sting  is  driven 
into  them  with  speedily  fatal  results.  It  is  doubtful  if  the 
poison  causes  death  in  man,  but  the  sting  of  some  of  the 


'.—Scorpion,  showing  pincer-like  mouth- 
parts  and  spine-tipped  tail. 


ARTHROPODS.  CLASS  ARACHN1DA       135 

larger  species,  which  measure  five  or  six  inches  in  length, 
may  produce  certain  disorders  chiefly  affecting  the  circula- 
tion. In  this  country  there  are  upward  of  thirty  species, 
most  of  which  are  comparatively  small. 

130.  The  harvestmen. — The  harvestmen  or  daddy-long- 
legs are  small-bodied,  long-legged  creatures  which  resemble 
in  general  appearance  several  of  the  spiders.     They  differ 
from  them,  however,  in  the  possession  of  claws  correspond- 
ing to  the  smaller  ones  of  the  scorpion,  and  in  their  method 
of  respiration,  which  is  similar  to  that  of  insects.     During 
the  day  they  conceal  themselves  in  dark  crevices  or  stride 
slowly  about  in  shaded  places ;  but  at  night  they  emerge 
into  more  open  districts  and  capture  small  insects,  from 
which  they  suck  the  juices. 

131.  The  spiders. — The  spiders  are  world-wide  in  their 
distribution,  and  are  a  highly  interesting   group,  owing 
chiefly  to  their  peculiar  habits.     Examining  any  of  our 
familiar  species,  it  will  be  seen  that  the  united  head  and 
thorax  are  separated  by  a  narrow  stalk  from  the  usually 
distended  abdomen.     To  the  under  side  of  the  former  are 
attached  four  pairs  of  long  legs,  a  pair  of  feelers,  and  the 
powerful  jaws  supplied  with  poison-sacs,  while  eight  shin- 
ing eyes  are  borne  on  the  top  of  the  head.     On  the  abdo- 
men, behind  the  last  pair  of  legs,  are  small  openings  into 
the  lung  cavities  which  contain  a  number  of  vascular,  leaf- 
like  projections  known  as  lung-books.     In  some  species 
a  well-marked  system  of  tracheae  are  also  present.     At  the 
hinder  end  of  the  body  are  four  or  six  little  projections, 
the  spinnerets,  each  of  which  is   perforated  with   many 
holes.     Through  these  the  secretion  from  the  glands  be- 
neath is  squeezed  out  in  the  form  of  excessively  delicate 
threads,  often  several  hundred  in  number,  which  harden  on 
exposure  to  the  air.     According  to  the  use  for  which  these 
are  intended,  they  may  remain  a  tangled  mass  or  become 
united  into  one  firm  thread  ;  and  according  to  the  habits 
of  the  animal,  they  may  be  used  for  enclosing  their  eggs, 

10 


136  ANIMAL  FORMS 

for  lining  their  burrows,  or  for  the  construction  of  webs  of 
the  most  diverse  patterns. 

132.  The  habits  of  spiders.— Many  species  of  spiders,  some 
of  which  are  familiar  objects  in  fields  and  houses,  construct 
sheets  of  cobweb  with  a  tube  at  one  side  in  which  they  may 


Pie.  83.— A  tarantula-spider  (Eurypelma  lentzii).    Natural  size.    Photograph  by 
A.  L.  MELANDER  and  C.  T.  BRUES. 

lie  in  wait  for  their  prey  or  through  which  they  may  escape 
in  times  of  danger.  In  the  webs  of  the  common  orb-  or 
wheel-weavers  several  radial  lines  are  first  constructed,  and 
upon  these  the  female  spider  spins  a  spiral  web.  Resting 
in  the  center  of  this  or  at  the  margin,  with  her  foot  on 
some  of  the  radial  threads,  she  is  able  to  detect  the  slight- 
est tremor  and  at  once  to  rush  upon  the  entangled  captive. 
Some  of  the  bird-spiders  and  their  allies,  living  in  trop- 
ical America,  and  attaining  a  length  of  two  inches,  con- 
struct web-lined  burrows  in  the  ground.  From  these  they 
stalk  their  prey,  which  consists  of  various  insects  and  even 


ARTHROPODS.  CLASS  ARACHNIDA 


137 


small  birds.  These  are  almost  instantly  killed  by  the  poison- 
fangs,  and  are  then  carried  to  the  burrow,  where  the  juices 
of  the  body  are  extracted. 

The  trap-door  spiders  of  the  southwestern  section  of  the 
United  States  also  dig  tunnels,  which  they  cover  with  a 
closely    fitting    lid    com- 
posed of  earth.      Raising  v     ,t 
this    they    come    out   in          w$ MjS8aSSf$^*~ 
search   of  insects,  but  if 
sought  in  turn,  they  dash 
into  the  burrow,  closing 
the  door  after  them,  and 
holding  it  with  such  firm- 
ness that  it  is  rarely  forced 
open.     If  this  should  hap- 
pen, there  are  sometimes 
blind    passage-ways,    also 
closed    with     trap-doors, 
which   usually  baffle   the 
pursuer. 

Finally,  there  are 
among  the  thousand  spe- 
cies of  spiders  in  the  United  States  a  considerable  propor- 
tion which  construct  no  definite  web.  Many  of  these  may 
be  seen  darting  about  in  the  sunshine  on  old  logs  and 
fences,  often  trailing  after  them  a  thread  which  may  sup- 
port them  if  they  fall  in  their  active  leaping  after  in- 
sects. 

133.  Breeding  habits. — The  male  spiders  are  usually  much 
smaller  than  the  females,  and  some  species  are  only  one- 
fifteenth  as  long  as  the  female  and  one  one-hundredth  of 
its  weight.  They  are"  usually  more  brilliantly  colored,  more 
active  in  their  movements,  yet  rarely  spinning  their  own 
webs  and  capturing  their  own  food,  preferring  to  live  at 
the  expense  of  the  female.  At  the  breeding  season  the 
males  of  several  species  make  a  most  interesting  display 


FIG.  84.— Trap-door  spider  and  burrow 
( C(eniza). 


138  ANIMAL  FORMS 

of  their  colors,  activity,  and  gracefulness  before  the  females ; 
and  the  latter,  after  watching  these  exhibitions,  are  said  to 
select  the  one  who  has  "  shown  off  "  in  the  most  pleasing 
fashion.  The  life  after  this  may  be  stormy,  resulting  in 
the  death  of  the  male ;  but  ordinarily  the  results  are  not 
so  disastrous,  and  in  a  little  while  the  female  deposits  her 
eggs  in  cases  which  she  spins.  In  these  the  young  develop, 
sometimes  wintering  here,  and  emerging  in  the  spring  to 
scamper  about  in,  search  of  food,  or  to  drift  through  the 
air  to  more  favorable  spots  on  fluffy  masses  of  cobweb. 

Few  groups  of  animals  are  more  interesting  objects  of 
study  and  more  accessible.  Their  bites  are  rarely  more 
serious  than  those  of  the  mosquito — never  fatal ;  and  a 
careful  study  of  any  species,  however 
common,  will  undoubtedly  bring  to 
light  many  interesting  and  unknown 
facts. 

134.  The  mites  and  ticks.— The 
mites  and  ticks  are  the  simplest  and 
among  the  smallest  of  the  animals 
belonging  to  this  group.  To  the  at- 
tentive observer  they  are  rather  com- 
mon objects,  with  homes  in  very  dif- 
ferent situations.  Some  occur  on  liv- 
FIG.  85.-The  itch-mite  (Sar-  jng  and  decaying  vegetation,  in  old 

coptes  scabei).  «       -,  •»  •,         ,1 

flour  and  unrefined  sugar,  while  oth- 
ers live  in  fresh  water  and  a  few  in  the  sea.  Almost  all 
tend  toward  parasitism.  Some  of  the  insects  which  they 
pierce  and  destroy  are  a  pest  to  man,  but  on  the  other  hand 
some  are  intolerable  owing  to  the  diseases  they  produce. 

As  to  other  parasitic  organisms,  degradation  of  structure 
is  manifest.  The  respiratory  system,  so  important  to  the 
active  life  of  the  insects,  may  be  absent,  the  animal  breath- 
ing through  its  skin.  The  circulatory  system  may  be  want- 
ing, the  blood  occupying  spaces  among  the  various  organs 
being  swept  about  by  the  animal's  movements.  And  many 


ARTHROPODS.    CLASS  ARACHNIDA 


139 


other  peculiarities   have  arisen  which  fit  them  for  their 
different  modes  of  life. 

135.  The  king  crab  (Limulus).— The  king  crab  may  be 
found  crawling  over  the  bottom  or  plowing  its  way  through 
the  sand  and  mud  in  many  of  the  quiet  bays  from  Maine 
to  Florida.  The  large  head  and  thorax  of  these  animals 
are  united  into  a  horse- 
shoe-shaped piece,  be- 
hind which  lies  the 
triangular  abdomen. 
On  the  curved  front 
surface  of  the  former 
are  a  pair  of  small  me- 
dian eyes,  and  farther 
outward  are  two  larger 
compound  ones.  On 
the  ventral  side  are 
six  pairs  of  append- 
ages, instrumental  in 
capturing  and  tearing 
the  small  animals  that 
serve  as  food,  and 
functioning  in  con- 
nection with  the  ter- 
minal spine  as  locomo- 
tor  organs.  On  the 
ventral  surface  of  the  abdomen  are  numerous  plate-like  flaps 
which  serve  in  respiration,  and  in  the  imperfect  swimming 
movements  in  which  these  animals  occasionally  indulge. 

These  relatively  large  and  clumsy  creatures  are  the  rem- 
nant of  a  great  number  of  strange,  uncouth  animals  that  in- 
habited the  earth  in  past  ages.  Many  of  them  show  a  close 
resemblance  to  the  scorpions.  The  anatomy  and  develop- 
ment also  show  certain  points  of  resemblance,  and  by  some 
are  thought  to  give  us  an  idea  of  the  ancient  type  of  spider- 
like  animal  from  which  the  modern  forms  have  descended. 


FIG.  86.— The  king  or  horseshoe  crab  (Limulus 
polyphemus). 


CHAPTER  XII 

ECHINODERMS 

136.  General  characters. — The  division  of  the  echino- 
derms  includes  the  starfishes,  sea-urchins,  serpent-  or  brittle- 
stars,  sea-cucumbers,  and  crinoids  or  sea-lilies.     All  are  ma- 
rine forms,  and  constitute  a  conspicuous  portion  of  the 
animals  along  almost  any  coast  the  world  over.     From 
these  shallow-water  situations  they  extend  to  the  greatest 
depths  of  the  ocean,  and  the  bodily  form  possesses  a  great 
number  of  variations,  adapting  them  to  lives  under  such 
diverse  conditions;  and  yet  there  is  perhaps  no  group  of 
organisms  so  clearly  defined  or  exhibiting  so  close  a  resem- 
blance throughout.     At  one  time  it  was  thought  that  their 
radial  symmetry  was  an  indication  of  a  close  relationship 
to  the  ccelenterates,  but  more  careful  study  has  shown  them 
to  be  much  more  highly  developed  than  this  latter  group, 
and  widely  separated  from  it.     A  skeleton  is  almost  always 
present,  consisting  of  a  number  of  calcareous  plates  embed- 
ded in  the  body-wall,  and  often  supporting  numbers  of  pro- 
tective spines,  which  fact  has  given  to  the  group  the  name 
Echinoderm,  meaning  hedgehog  skin. 

137.  External  features.— The  body  of  a  starfish  (Fig.  87) 
consists  of  a  more  or  less  clearly  defined  disk,  from  which 
the  arms,  usually  five  in  number,  radiate  like  the  spokes 
of  a  wheel.     At  the  center  of  the  under  side  the  mouth  is 
located,  and  from  it  a  deep  groove,  filled  with  a  mass  of 
tubular  feet,  extends  to  the  tip  of  each  arm.     Innumerable 
calcareous  plates  firmly  embedded  in  the  body-wall  serve 

140 


ECHINODERMS  141 

for  the  protection  of  the  internal  organs,  and  at  the  same 
time  admit  of  considerable  movement. 
1     In  the  brittle-stars  (Fig.  88)  the  central  disk  is  much 
more  sharply  defined  than  in  the  preceding  forms,  and  the 
long  snake-like  arms  are  capable  of  a  very  great  freedom  of 
movement,  enabling  the  animal  to  glide  over  the  sea-bottom, 
or  through  the  crevices  of  the  rocks,  at  a  surprising  rate. 
In  several  species,  otherwise  closely  resembling  those 


FIG.  87.— Starfish  (Asterias  ocracea),  ventral  view.    One-half  natural  size. 


in  Fig.  88,  the  arms  divide  repeatedly.  These  are  the  so- 
called  basket-stars,  living  in  the  deeper  waters  of  the  sea, 
where  they,  like  other  brittle-stars,  act  as  scavengers  and 
devour  large  quantities  of  decomposing  plant  or  animal 
remains. 

At  first  sight  the  globular  spiny  sea-urchins  (Fig.  90) 
would  scarcely  be  recognized  as  close  relatives  of  the  star- 
fishes. A  closer  examination,  however,  shows  the  mouth  to 
be  located  on  the  under  side  of  the  body  ;  from  it  five  rows 
of  feet  radiate  and  terminate  close  to  the  center  of  the 
dorsal  side,  and  the  arrangement  of  the  plates  forming  the 


142 


ANIMAL  FORMS 


skeleton  indicate  that  the  sea-urchin  is  comparable  to  a 
starfish,  with  its  dorsal  surface  reduced  to  insignificant 
proportions. 

In  the  sea-urchins  the  calcareous  plates  possess  a  great 
regularity,  and  are  so  closely  interlocked  that  they  prevent 


FIG.  88.— Brittle-  or  serpent-stars  (species  undetermined).    Natural  size. 

any  motion  of  the  body-wall.  Also,  each  plate  is  usually 
provided  with  highly  developed  spines,  movable  upon  a  ball- 
and-socket  joint.  These  spines  serve  for  locomotion,  and, 
in  some  instances,  for  conveying  food  to  the  mouth.  A 
considerable  number  of  sea-urchins  show  an  irregularity  in 
form  which  destroys  to  a  corresponding  degree  the  radial 
symmetry.  This  is  due  to  various  causes,  but  especially  to 
a  compression  of  the  body,  which,  in  the  "sand-dollars," 


ECHIXODERMS  143 

has  resulted  in  the  production  of  a  thin,  cake-like  form 
(Fig.  91). 

If  the  spherical  body  of  a  sea-urchin  were  to  be  stretched 
in  the  direction  of  a  line  joining  the  mouth  and  the  center 


FIG.  89.— Basket-star  (Astrophyton).    One-half  natural  size. 

of  the  dorsal  surface,  a  form  resembling  a  sea-cucumber 
(Fig.  92)  would  be  the  result.  These  latter  organisms  live 
among  crevices  of  the  rocks,  embedded  in  the  mud  or  bur- 
rowing in  the  sand  at  the  bottom  of  the  sea.  In  such  situa- 
tions they  are  well  protected,  and  a  highly  developed  skele- 
ton, such  as  that  of  the  sea-urchin,  would  not  only  be  of 
little  value,  but  a  positive  hindrance  to  locomotion.  The 
skeleton,  therefore,  is  much  reduced,  consisting  of  a  few 
scattered  calcareous  plates  embedded  in  the  fleshy  body- 
wall.  Another  peculiar  feature  is  almost  universally  pres- 
ent, in  the  form  of  a  circlet  of  tentacles  surrounding  the 
mouth,  which  serve  either  for  the  purpose  of  respiration, 
for  locomotion,  or  to  convey  food  to  the  mouth. 

A  very  good  imitation  of  the  general  plan  of  a  sea-lily 
or  crinoid  (Fig.  93)  could  be  made  by  attaching  a  serpent- 


144 


ANIMAL  FORMS 


star,  especially  one  of  the  basket-stars,  by  its  dorsal  side 
to  a  stalk.  In  the  crinoids  the  numerous  branches  of  the 

arms  are  compara- 
tively short,  and  in 
the  arrangement  of 
the  internal  organs 
there  are  numer- 
ous differences,  but 
for  all  that  the  re- 
semblance of  these 
organisms  to  the 
other  echinoderms 
is  undoubted. 

138.  Haunts. — 
The  greater  num- 
ber of  starfishes 
occur  alongshore, 
slowly  crawling 
about  in  search  of 
food,  or  concealed 
in  dark  crevices  of 

the  rocks,  where  they  may  often  be  found  as  the  tide  goes 
out,  and  we  know  that  in  gradually  lessening  numbers  other 
species  lead  similar  lives  at  different  levels  far  down  in  the 
dark  and  gloomy  depths.  In  these  same  locations  the  sea- 
urchins  occur,  sometimes  singly,  but  more  usually  associa- 
ted in  great  numbers,  several  species  excavating  hollows  in 
the  rocks,  within  which  they  obtain  protection.  The  brit- 
tle-stars and  sea-cucumbers  may  also  be  found  occasionally 
in  open  view,  but  more  often  they  make  their  way  about  in 
search  of  food  buried  in  the  sand.  The  crinoids  are  usual- 
ly inhabitants  of  deeper  water,  where  they  are  found  asso- 
ciated often  in  great  numbers.  A  few  species  upon  attain- 
ing the  adult  condition  separate  from  the  stalk,  and  are 
able  to  move  about  (Fig.  95),  but  the  remaining  species 
never  shift  their  position. 


FIG.  90. — Sea-urchin  (Strongylocentrotus  pitrpuratus). 
Natural  size. 


ECHIXODERMS  145 

139.  The  organs  of  defense  and  repair  of  injury. — As  we 
have  seen,  the  body-wall  of  the  echinoderms  is  provided 
with  a  series  of  plates,  often  bearing  spines  which  serve  as 
organs  of  defense,  and  to  protect  the  internal  organs.  The 
starfishes  and  sea-urchins  also  possess  numerous  modified 
spines  (pedicellarid)  scattered  over  the  surface  of  the  body, 
which  have  the  form  of  miniature  birds'  beaks,  fastened  to 
slender  muscular  threads.  During  life  these  jaws  continu- 
ally open  and  close,  and  it  is  said  they  clean  the  body  of 
debris  that  settles  on  it ;  but  on  the  other  hand  there  are 
several  reasons  for  the  belief  that  they  also  act  as  organs 
of  defense.  Thus  protected,  the  natural  enemies  of  echino- 
derms appear  to  be  relatively  few,  and  are  confined  chiefly 
to  some  of  the  fishes  whose  teeth  are  especially  modified 
for  crushing  them.  In  this 
way,  and  owing  to  the  action 
of  the  breakers,  they  suffer 
frequent  injury,  but  many 
species  exhibit  to  a  remark- 
able degree  the  ability  to  re- 
generate lost  parts.  Experi- 
ments show  that  if  all  the 
arms  of  a  starfish  be  separa- 
ted from  the  disk  the  latter 
will  within  two  or  three 
months  renew  the  arms  ;  and  FlG-  »i.-sand-doiiar.  a  flat  sea-urchin. 

.  Natural  size. 

a  single  arm  with  a  part  of 

the  disk  is  able  to  renew  the  missing  portions  in  about  the 

same  length  of  time. 

The  brittle-stars,  as  their  name  indicates,  are  usually  ex- 
cessively delicate,  often  dropping  all  of  their  arms  upon  the 
slightest  provocation ;  but  here  again  the  ability  is  present 
to  develop  the  lost  portions. 

Sea-cucumbers  resent  rough  treatment  by  vigorously 
contracting  their  muscular  walls  and  removing  from  the 
body  almost  the  entire  digestive  tract,  the  respiratory  tree, 


146 


ANIMAL  FORMS 


and  a  portion  of  the  locomotor  system ;  but  some  species,  at 
least,  renew  them  again.  In  some  of  the  starfishes  and 
brittle-stars  portions  of  the  body 
appear  to  be  voluntarily  de- 
tached and  to  develop  into  new 
individuals,  and  it  is  thought 
that  such  self-mutilation  is  a 
normal  method  of  reproduction. 
140.  Locomotor  system. — One 
of  the  most  characteristic  and 
remarkable  features  of  the  echi- 
noderms  is  the  water- vascular 
system,  a  series  of  vessels  con- 
taining water  which  serve  in  the 
process  of  locomotion.  Their 
arrangement  and  mode  of  opera- 
tion are,  with  slight  modifica- 
tions, the  same  throughout  the 
group,  and  may  be  readily  un- 
derstood from  their  study  in 
the  starfish. 

On  the  dorsal  surface  of  a 
starfish,  in  the  angle  between 

two  of  the  arms,  is  a  round,  slightly  elevated,  calcareous 
plate,  the  madreporic  body  (Fig.  95,  m.p.),  which  under 
the  microscope  appears  full  of  holes,  like  the  "  rose  "  of  a 
watering-pot.  This  connects  with  a  tube  that  passes  to 
the  opposite  side  of  the  body,  where  it  enters  a  canal 
completely  encircling  the  mouth.  On  this  ring-canal  a 
number  of  sac-like  reservoirs  with  muscular  walls  are  at- 
tached, and  from  it  a  vessel  extends  along  the  under  sur- 
face of  each  arm  from  base  to  tip.  Each  of  these  radial 
water-mains  gives  off  numerous  lateral  branches  that  open 
out  into  small  reservoirs  similar  to  those  located  on  the 
ring-canal,  and  a  short  distance  beyond  communicate 
through  the  wall  of  the  body  with  one  of  the  numerous 


PIG.  92.— Sea-cucumber  {Cucu- 
maria  sp.).    Natural  size. 


ECHINODERMS 


147 


tube-feet,  which,  as  we  have  seen,  are  slender  tubular  or- 
gans, many  in  number,  filling  the  grooves  on  the  ventral 
surface  of  each  arm.  This  entire  system  of  tubes  and 
reservoirs  is  full  of  water,  taken  in,  it  is  said,  through  the 
perforated  plate,  and,  when  the  starfish  wishes  to  advance, 
many  of  the  little  reservoirs  con- 
tract, forcing  water  into  the  cav- 
ity of  the  feet,  with  which  they 
are  in  communication,  thus  ex- 
tending the  extremity  of  the  tubes 
a  considerable  distance.  The 
terminal  sucker  of  each  foot,  act- 
ing upon  the  same  principle  as 
those  on  the  cuttlefish,  attaches 
firmly  to  some  foreign  object, 
whereupon  the  muscles  of  the 
foot  contract,  drawing  the  body 
toward  the  point  of  attachment. 
This  latter  movement  is  similar 
to  that  of  a  boatman  pulling  him- 
self to  land  by  means  of  a  rope 
fastened  to  the  shore.  When  the 
shortening  of  the  tube-feet  has 
ceased,  the  sucking  disks  release 
their  attachment,  project  them- 
selves again,  and  this  process  is 
repeated  over  and  over.  At  all 
times  some  of  the  feet  are  con- 
tracting, and  a  steady  advance  of 
the  body  is  the  result. 

This   method    of    locomotion 

also  obtains  in  the  sea-urchins  and  cucumbers,  but  in  the 
serpent-stars  the  tube-feet  have  become  modified  into  feel- 
ers, and  the  animal  moves,  often  rapidly,  by  means  of  twist- 
ing movements  of  the  arms.  The  feet  have  this  character 
also  in  the  crinoids,  where  the  animal  is  generally  without 


PIG.  93.— Sea-lily  or  crinoid. 


148  ANIMAL  FORMS 

the  power  of  locomotion.  In  some  of  the  sea-cucumbers 
five  equidistant  rows  of  tube-feet  extend  from  one  end  of 
the  body  to  the  other,  and  the  animal  crawls  worm-like 
upon  any  side  that  happens  to  be  down ;  but  certain  spe- 
cies living  in  the  sand, 

•••£»&£&*  where    tube  -  feet    will 

not  work  satisfactorily, 
have  lost  all  traces  of 
them,  and  creep  like  an 
earthworm  from  place 
to  place.  In  all  the 
sea-cucumbers  the  feet, 
situated  nearthe  mouth, 
"^'4^^''^^^''  have  been  curiously 

F,,.,, -An  unattached  crinoid(^rf0,0.    One-    modified   to   form  a  cir- 

half  natural  size.  clet  of  tentacles,  which 

range  in  form  from 

highly  branched  to  short  and  thick  structures,  and  in  func- 
tion from  respiratory  organs  and  those  of  touch  to  con- 
trivances for  scooping  up  sand  and  conveying  it  to  the 
mouth. 

141.  Food  and  digestive  system. — In  the  echinoderms  the 
body-wall  is  comparatively  thin  (Fig.  95),  and  encloses  a 
great  space,  the  body-cavity,  in  which  the  digestive  and  re- 
productive organs  are  contained.  As  the  former  in  various 
species  is  adapted  for  acting  upon  very  different  kinds  of 
food,  it  shows  many  modifications  ;  but  there  are  a  few  prin- 
cipal types  which  may  be  briefly  considered. 

In  the  starfishes  the  mouth  enters  almost  directly  into 
the  cardiac  division  of  the  stomach,  a  capacious,  thin-walled 
sac,  much  folded  and  packed  away  in  the  disk  and  bases  of 
the  arms  (Fig.  95,  b).  This  in  turn  leads  into  the  second 
pyloric  portion  («),  with  thicker  walls  and  dorsal,  to  the 
first,  from  which  a  short  intestine  leads  to  the  exterior, 
near  the  center  of  the  disk.  Another  conspicuous  and  im- 
portant feature  is  the  so-called  liver,  consisting  of  a  pair 


ECHINODERMS  149 

of  closely  branched,  fluffy  glands  (I),  extending  the  entire 
length  of  each  arm  and  opening  into  the  pyloric  stomach. 

The  starfishes  are  carnivorous  and  highly  voracious,  de- 
vouring large  numbers  of  barnacles  and  mollusks  which  hap- 
pen in  their  path.  If  these  are  small  and  free  they  are 
taken  directly  into  the  stomach,  but  when  one  of  relatively 
large  size  is  encountered  the  starfish  settles  down  upon  it, 
and,  slowly  pushing  the  cardiac  stomach  through  the  mouth, 
envelops  it  in  the  folds.  Digestive  fluids  are  now  poured 
over  it,  and  the  victim  is  speedily  despatched  and  in  a  partly 
digested  condition  is  gradually  absorbed  into  the  body,  leav- 


FIG.  95.— Dissection  of  starfish  to  show  :  a,  pyloric  stomach  ;  b,  bile-ducts  (above), 
cardiac  stomach  (below) ;  b.c.,  body-cavity ;  /,  feet ;  g,  spines ;  i,  intestine ; 
/,  liver ;  m,  mouth  ;  m.p.,  madreporic  plate  ;  /',  reservoir ;  r.c.,  ring  canal ; 
r.m.,  stomach  retractor  muscle  ;  r.v.,  radial  vessel ;  s,  stone  canal ;  t,  respira- 
tory tree. 

ing  the  shell  and  other  indigestible  matters  upon  the  exte- 
rior. Oysters  and  clams  close  their  shells  when  thus  attacked, 
but  a  steady,  continuous  pull  on  the  part  of  the  starfish 
finally  opens  them,  and  the  stomach  is  spread  over  the  fleshy 
portions  with  speedily  fatal  results.  In  the  interior  of  the 
body  the  food  is  transferred  to  the  pyloric  stomach,  sub- 
jected to  the  action  of  the  liver,  and  when  completely  dis- 
solved is  borne  to  all  parts  of  the  body. 


150  ANIMAL   FORMS 

The  digestive  system  of  the  starfishes,  with  its  various 
subdivisions  and  appendages,  is  in  some  respects  more  com- 
plicated than  in  the  other  classes.  This  is  most  strikingly 
the  case  with  the  serpent-stars,  where  the  entire  system  for 
disposing  of  the  minute  animals  and  plants  on  which  it 
feeds  consists  of  a  simple  sac  communicating  with  the 
exterior  by  a  single  opening — the  mouth. 

In  the  sea-cucumbers  large  quantities  of  sand  are  taken 
into  the  body,  and  the  minute  organisms  and  organic  mat- 
ter are  digested  from  it.  In  the  sea-urchins  the  mouth  is 
provided  with  five  teeth,  and  the  food  consists  of  minute 
bits  of  seaweeds,  which  these  snip  off.  Such  diets  evidently 
require  a  comparatively  simple  digestive  apparatus,  for  in 
both  it  consists  throughout  its  whole  extent  of  a  tube  of 
equal  caliber,  in  which  the  various  divisions  of  esophagus, 
stomach,  and  intestine  are  little,  if  at  all,  defined.  This 
is  usually  somewhat  longer  than  the  body,  and  therefore 
thrown  into  several  loops ;  and  in  the  sea-cucumbers  its  last 
division  is  expanded  and  furnished  with  more  highly  mus- 
cular walls,  which  aid  in  respiration. 

142.  Development.— With  but  a  few  exceptions,  the  eggs 
of  the  echinoderms  are  laid  directly  in  the  surrounding 
water,  and  for  many  days  the  exceedingly  minute  young 
are  borne  great  distances  in  the  tidal  currents.  During 
this  period  they  show  no  resemblance  to  their  parents,  and 
only  after  undergoing  remarkable  transformations  do  they 
assume  their  permanent  features.  In  every  case  they  have 
a  five-rayed  form  in  early  youth,  but  in  several  species  of 
starfishes  additional  arms  develop  until  there  may  be  as 
many  as  twenty  or  thirty. 


CHAPTER    XIII 

THE    CHOBDATES 

143.  General  characters.— Up  to  the  present  time  we  have 
been  studying  the  representatives  of  a  vast  assemblage  of 
animals  whose  skeletons,  if  they  have  any  at  all,  are  located 
on  the  outside  of  the  body.  In  the  corals,  the  mighty  com- 
pany of  arthropods,  and  the  echinoderms,  it  is  external.  On 
the  other  hand,  we  shall  find  that  the  animals  we  are  now 
about  to  consider,  the  fishes,  frogs,  lizards,  birds,  and  mam- 
mals, are  in  possession  of  an  internal  skeleton.  In  some  of 
the  simpler  fishes  and  in  a  number  of  more  lowly  forms  (Fig. 
96)  it  is  exceedingly  simple,  and  consists  merely  of  a  gristle- 
like  rod,  the  notochord  (Fig.  98,  nc),  extending  the  length 
of  the  body  and  serving  to  support  the  nervous  system,  which 
is  always  dorsal.  This  is  also  the  type  of  skeleton  found  in 
the  young  of  the  remaining  higher  animals,  but  as  they  grow 
older  the  notochord  gives  way  to  a  more  highly  developed 
cartilaginous  or  bony,  jointed  skeleton,  the  vertebral  column. 

In  the  young  of  all  these  back-boned  or  chordate  ani- 
mals, the  sides  of  the  throat  are  invariably  perforated  to 
form  a  number  of  gill-slits.  In  the  lower  forms  these  per- 
sist and  serve  as  respiratory  organs,  but  in  the  higher  ani- 
mals they  disappear  in  the  adult.  The  chordates  are  thus 
seen  to  be  distinguished  by  the  possession  of  a  dorsal  nerv- 
ous cord  supported  by  an  internal  skeleton  and  by  the 
presence  of  gill-slits,  characters  which  separate  them  widely 
from  all  invertebrates. 

The  chordates  may  be  divided  into  ten  classes,  seven  of 
11  151 


152 


ANIMAL  FORMS 


which  (the  lancelets,  lampreys,  fishes,  amphibians,  reptiles, 
birds,  and  mammals)  are  true  vertebrates,  while  the  others 
embrace  several  peculiar  animals  of  much  simpler  organiza- 
tion. 

144.  The  ascidians. — Among  the  latter  are  a  number  of 
remarkable  species  belonging  to  the  class  of  ascidians  or 

sea-squirts  (Fig.  96). 
These  are  abundantly 
represented  along  our 
coasts,  and  are  readily 
distinguished  by  their 
sac -like  bodies,  which 
are  often  attached  at 
one  end  to  shells  or 
rocks.  On  the  opposite 
extremity  two  openings 
exist,  through  which  a 
constant  stream  of  water 
passes,  bearing  minute 
organisms  serving  as 
food.  When  disturbed 
they  frequently  expel 
the  water  from  these 
pores  with  considerable 
force,  whence  the  name 
"  sea-squirt."  While 
many  lead  solitary  lives, 

numerous  individuals  of  other  species  are  often  closely 
packed  together  in  a  jelly-like  pad  attached  to  the  rocks, 
and  others  not  distantly  related  are  fitted  to  float  on  the 
surface  of  the  sea. 

The  young  when  hatched  resemble  small  tadpoles  both  in 
their  shape  and  in  the  arrangement  of  some  of  the  more 
important  systems  of  organs.  For  a  few  hours  each  swims 
about,  then  selecting  a  suitable  spot  settles  down  and  ad- 
heres for  life.  From  this  point  on  degeneration  ensues. 


FIG.  96.— Ascidian  or  sea-squirt. 


THE  CHORDATES  153 

The  tail  disappears,  and  with  it  the  notochord  and  the 
greater  part  of  the  nervous  system.  The  sense-organs  van- 
ish, the  pharynx  becomes  remodeled,  and  numerous  other 
changes  occur,  leaving  the  animal  in  its  adult  condition, 
with  little  in  its  motionless,  sac-like  body  to  remind  one  of 
a  vertebrate. 

145.  The  vertebrates. — Since  the  remainder  of  this  vol- 
ume is  concerned  with  the  vertebrates  it  will  be  well  at  the 
outset  to  gain  some  knowledge  of  their  more  important 
characteristics.  One  of  the  most  apparent  is  the  presence 
of  a  jointed  vertebral  column,  composed  of  cartilage  or 
bone,  which  supports  the  nervous  system.  To  it  are  also 
usually  attached  several  pairs  of  ribs,  two  pairs  of  limbs, 
either  fins,  legs,  or  wings,  and  in  front  it  terminates  in  a 
more  or  less  highly  developed  skull.  In  the  space  par- 
tially enclosed  by  the  ribs,  the  body-cavity,  a  digestive  sys- 
tem is  located,  which  consists  of  the  stomach  and  intestine, 
together  with  the  attached  liver  and  pancreas.  The  cir- 
culatory system  is  also  highly  organized,  and  consists  of  a 
muscular  heart,  arteries,  and  veins  which  ramify  through- 
out the  body.  Breathing,  in  the  aquatic  animals,  is  car- 
ried on  by  means  of  gills,  and  in  the  air-breathing  forms 
by  means  of  lungs,  which,  like  the  gills,  effect  the  removal 
of  carbonic-acid  gas  and  the  absorption  of  oxygen.  The 
nervous  system,  consisting  of  the  brain  situated  in  the 
head  and  the  spinal  cord  extending  through  the  body 
above  the  back-bone,  even  in  the  lower  vertebrates,  is  far 
more  complex  than  in  the  invertebrates.  The  sense-organs 
also  attain  to  a  high  degree  of  acuteness,  and  in  connec- 
tion with  the  highly  organized  nervous  system  enable  these 
forms  to  lead  far  more  varied  and  complex  lives  than  in 
any  of  the  animals  heretofore  considered. 


CHAPTER  XIV 

THE   FISHES 

146.  General  characters.— In  a  general  way  the  name  fish- 
is  applied  to  all  vertebrates  which  spend  the  whole  of  their 
life  in  the  water,  which  undergo  no  retrograde  metamor- 
phosis, and  which  do  not  develop  fingers  or  toes.  Of  other 
aquatic  chordates  or  vertebrates  the  ascidians  undergo  a 
retrograde  metamorphosis,  losing  the  vertebral  column,  and 
with  it  all  semblance  of  fish-like  form.  The  amphibians, 
on  the  other  hand,  develop  jointed  limbs  with  fingers  and 
toes,  instead  of  paired  fins  with  fin  rays.  A  further  com- 
parison of  the  animals  called  fishes  reveals  very  great  dif- 
ferences among  them — differences  of  such  extent  that  they 
cannot  be  placed  in  a  single  class.  At  least  three  great 
groups  or  classes  must  be  recognized :  the  Lancelets,  the 
Lampreys,  and  the  True  Fishes.  The  general  characters  of 
all  these  groups  will  be  better  understood  after  the  study 
of  some  typical  fish,  that  is  one  possessing  as  many  fish-like 
features  as  possible,  unmodified  by  peculiar  habits.  Such  an 
example  is  found  in  the  bass,  trout,  or  perch.  In  either  fish 
the  pointed  head  is  united,  without  any  external  sign  of  a 
neck,  to  the  smooth,  spindle-shaped  body,  which  is  thus  fitted 
for  easy  and  rapid  cleaving  of  the  water  when  propelled  by 
the  waving  of  the  powerful  tail  (Fig.  97).  A  keel  also  has 
been  provided,  enabling  the  fish  to  steer  true  to  its  course. 
This  consists  of  .folds  of  skin  arising  along  the  middle  line  of 
the  body,  supported  by  numerous  bony  spines  or  cartilaginous 
154 


THE  FISHES  155 

rays.  These  are  the  unpaired  fins,  as  distinguished  from 
the  paired  ones,  which  correspond  to  the  limbs  of  the  higher 
vertebrates.  In  the  bass  or  perch  the  latter  are  of  much 
service  in  swimming,  and  are  also  most  important  organs  in 
directing  the  course  of  the  fish  upward  or  downward,  or  for 


FIG.  97.— Yellow  perch  (Perca  Jlavescem).   df,  dorsal  fins  ;  pc.  pectoral  fin  ;  pf,  pelvic 
fin  ;  v,  ventral  fin. 

aiding  the  tail  in  changing  the  course  from  side  to  side ; 
or  they  may  be  used  to  support  the  animal  as  it  rests  upon 
the  bottom  in  wait  for  food  ;  and,  finally,  they  may  serve  to 
keep  the  body  suspended  at  a  definite  point. 

In  addition  to  an  internal  skeleton  the  bass  or  perch, 
like  the  greater  number  of  fishes,  is  more  or  less  enclosed 
and  protected  by  an  external  one,  consisting  of  a  beautifully 
arranged  series  of  overlapping  scales,  which  afford  protec- 
tion to  the  underlying  organs,  and  at  the  same  time  admit 
of  great  freedom  of  movement.  These  usually  consist  of  a 
horny  substance,  to  which  lime  is  sometimes  added,  and 
are  peculiar  modifications  of  the  skin,  something  like  the 
feathers,  nails,  and  hoofs  of  higher  forms. 

147.  The  air-bladder. — Xaturally  a  fish's  body  is  heavier 
than  the  water  in  which  it  lives,  and  there  are  reasons  for 
thinking  that  the  air-bladder  (Fig.  106,  a.bl.)  acts  in  the 


156  ANIMAL  FORMS 

bass  and  perch  and  many  other  fishes  as  a  float  to  enable 
them,  without  much  effort,  to  remain  suspended  at  a  defi- 
nite level.  By  compressing  this  sac,  partly  by  its  own  mus- 
cles and  partly  by  those  of  the  body-wall,  the  bulk  of  the 
fish  is  made  less,  and  it  sinks ;  upon  the  relaxation  of  these 
same  muscles  the  body  expands  and  rises  again.  Deep-sea 
fishes,  when  brought  to  the  surface,  where  the  pressure  is 
relatively  slight,  are  found  with  their  air-bladders  so  dis- 
tended that  they  can  not  sink  again,  and  the  float  of  surface 
fishes  would  be  as  useless  if  they  were  to  be  carried  into  the 
depths  below,  so  that  such  fishes  are  compelled  to  keep 
within  tolerably  definite  limits  of  depth.  Morphologically 
considered,  the  air-bladder  is  a  modified  or  degenerate  lung, 
and  in  many  fishes  it  is  lost  altogether. 

148.  Respiration. — Looking  down  the  throat  of  the  perch, 
or  any  other  fish,  a  series  of  slits  (the  gill-openings),  usually 
four  or  five  in  number,  may  be  seen  on  each  side  communi- 
cating with  the  exterior.     In  the  sharks  these  outer  open- 
ings are  readily  seen,  but  in  the  bony  fishes  they  open  into 
a  chamber  on  each  side  of  the  head,  covered  by  a  bony  plate 
or  gill-cover  that  is  open  behind.      On  raising  these  flaps 
the  gills  may  be  seen  composed  of  great  numbers  of  bright- 
red  filaments  attached  to  the  bars  between  each  slit.     Dur- 
ing life  the  fish  may  be  seen  to  open  its  mouth  at  regular 
intervals,  and,  after  gulping  in  a  quantity  of  water,  to  close 
it  again,  contracting  the  sides  of  the  throat  to  force  it  out 
of  the  gill-openings  and  over  the  gill-filaments  to  the  exte- 
rior.    During  this  process  the  blood  traversing  the  excess- 
ively thin  filaments  extracts  the  oxygen  from  the  water  and 
carries  it  to  other  parts  of  the  body. 

With  this  information,  let  us  return  to  the  study  of  the 
three  classes  of  fishes. 

149.  The  lancelet  (Branchiostoma). — The  lancelet,  some- 
times called  amphioxus  (Fig.  98),  the  type  of  the  class  Lepto- 
cardii,  is  a  little  creature,  half  an  inch  to  four  inches  long,  in 
the  different  species,  transparent  and  colorless,  living  in  the 


THE   FISHES 


157 


sand  in  warm  seas,  the  nine  species  known  being  found  in 
as  many  different  regions.  A  lancelet  may  be  regarded  as 
a  vertebrate  reduced  to  its  lowest  terms.  Instead  of  a 
jointed  back-bone,  it  has  a  cartilaginous  notochord,  running 
from  the  head  to  the  tail.  A  nervous  cord  lies  above  it, 
enclosed  in  a  membranous  sheath.  Xo  skull  is  present,  and 
the  nerve-cord  does  not  swell  into  a  brain.  There  are  no 
eyes  and  no  scales.  The  mouth  is  a  vertical  slit,  without 
jaws.  There  is  no  trace  of  the  shoulder-girdle  (shoulder- 
blade  and  collar-bone)  or  pelvis  (hip-bone)  from  which 


FIG.  98.— The  California  lancelet  ( Branchiostoma  californiense).    Twice  the  natural 
size,    g,  gills  ;  I,  liver  ;  m,  mouth  ;  n,  nerve-cord  ;  nc,  notochord. 

spring  the  paired  fins,  which,  in  true  fishes,  correspond  to 
arms  and  legs.  The  circulatory  system  is  fish-like,  but  there 
is  no  heart,  the  blood  being  driven  about  by  the  contraction 
of  the  walls  of  the  vessels.  Along  the  edge  of  the  back  and 
tail  is  a  rudimentary  fin,  made  of  fin-rays  connected  by  mem- 
brane. In  the  character  and  arrangement  of  its  organs  the 
lancelet  is  certainly  like  a  fish,  but  in  degree  of  develop- 
ment it  differs  more  from  the  lowest  fish  than  the  fish  does 
from  a  mammal. 

150.  Lampreys  (or  Cyclostomes). — The  class  of  lampreys 
stands  next  in  development  (Fig.  99).  The  notochord  gives 
way  anteriorly  to  a  cartilaginous  skull,  in  which  is  con- 
tained the  brain,  of  the  ordinary  fish  type.  There  are  eyes, 
and  the  heart  is  developed,  and  consists  of  an  auricle  and 
a  ventricle.  As  distinguished  from  the  true  fish,  the  lam- 
preys show  no  trace  whatever  of  limbs  or  of  the  bones 
which  would  support  them.  The  lov»  -r  u,  v  is  wholly  want- 
ing, the  mouth  being  a  roundish  sucking  lisk.  The  fins 


158 


AX  DIAL   FORMS 


are  better  developed,  but  of  the  same  structure  as  in  the 
lancelet.  There  is  no  bony  matter  in  the  skeleton,  and 
there  are  no  scales.  The  nasal  opening  is  single  on  the  top 
of  the  front  of  the  head. 

There  are  about  twenty-five  species  in  this  class.     Some 
of  them,  called  lampreys,  ascend  the  streams  from  the  sea 


FIG.  99. — Lampreys. 

in  the  spring  for  the  purpose  of  spawning.  The  young 
undergo  a  metamorphosis,  at  first  being  blind  and  tooth- 
less. The  adults  feed  mostly  on  the  blood  of  fishes,  which 
they  suck  after  scraping  a  hole  in  the  flesh  with  their  rasp- 
like  teeth.  The  others,  called  hag-fishes,  live  in  the  sea 
and  bore  into  the  bodies  of  other  fishes,  whose  muscles  they 
devour.  All  are  slender,  smooth,  and  eel-shaped. 

From  their  structure  and  a  few  fossil  remains  we  sup- 
pose that  these  eel-like  forms  existed  long  ago,  probably  be- 
fore the  more  highly  developed  sharks  and  bony  fishes  made 
their  appearance,  but  it  is  difficult  to  determine  whether 
their  simple  organization  is  of  such  long  standing  or  is  not 
in  part  the  result  of  semiparasitic  habits,  or  a  life  spent 


THE  FISHES  159 

largely  in  burrowing.  Like  the  lancelet  and  other  simple 
chordates,  they  are  of  the  greatest  interest  to  the  zoologist 
who  gains  from  them  some  idea  of  the  lowly  vertebrate 
forms  that  peopled  the  earth  long  ago. 

151.  True  fishes. — The  third  class,  Pisces  or  true  fishes, 
to  which  the  shark  as  well  as  the  bass  and  perch  belong  has 
a  well-developed  skeleton,  skull,  and  brain.     The  lower  jaw 
is  developed,  forming  a  distinct  mouth,  and  there  is  at  least 
a  shoulder-girdle  and  pelvis ;  although  the  fins  these  should 
bear  are  not  always  developed,  the  general  traits  are  those 
we  associate  with  the  fish.     Of  the  true  fishes,  there  are 
again  several  strongly  marked  groups,  usually  called  sub- 
classes.    Of  these,  three  chiefly  interest  us. 

152.  The  sharks  and  skates. — Very  early  in  the  life  of 
the  sharks  (Fig.  100)  and  skates  (SelacTiii  or  Elasmobranchii) 


FIG.  100.— Dogfish  (Squalus  acanthias).    One-seventh  natura 


a  notochord  appears,  similar  to  that  in  the  lancelet  and  the 
lampreys.  As  growth  proceeds  its  sheath  becomes  broken 
up  into  a  series  of  cartilaginous  rings,  which  thus  appear 
like  spools  strung  on  a  cord.  As  the  fish  grows  older  these 
"  spools  "  or  vertebrae  grow  solid,  cutting  the  notochord  into 
little  disks,  and  great  flexibility  is  thus  secured.  Cartilagi- 
nous appendages  also  grow  up  and  cover  the  spinal  nerve- 
cord  lying  above,  and  give  strength  to  the  unpaired  fins ; 
the  paired  fins  also  have  their  supports.  The  shoulder- 


160  ANIMAL   FORMS 

girdle  is  placed  behind  the  skull,  leaving  room  for  a  distinct 
neck  ;  strong  bars  of  cartilage  bear  the  gills ;  others  form  jaws 
to  carry  the  teeth ;  and  a  complex  skull  protects  the  brain 
and  sense-organs,  which  are  of  a  relatively  high  state  of  devel- 
opment. Throughout  life  the  skeleton  is  of  cartilage,  with 
perhaps  here  and  there  a  little  bone  where  greater  strength 
is  required.  Besides  these,  there  are  numerous  minor 
characters  which  the  student  will  readily  find  for  himself. 

The  sharks  and  skates  or  rays  live  chiefly  in  the  sea, 
and  some  reach  an  enormous  size,  the  largest  of  all  fishes. 
Some  are  very  ferocious  and  voracious ;  others  are  very  mild 
and  weak,  and  the  development  of  teeth  is  in  direct  pro- 
portion to  their  voracity  of  habit.  In  earlier  geologic  times 
there  were  many  more  species  of  them  than  now  exist. 

153.  The  lung-fishes.— The  lung-fishes  (Dipnoi)  are  pe- 
culiar forms  living  in  some  of  the  rivers  of  Australia  and 
the  tropical  regions  of  Africa  and  South  America.    In  these 
the  air-bladder  is  developed  as  a  perfect  lung.     During  the 
wet  season  they  breathe  like  other  fishes  by  means  of  gills, 
but  as  the  rivers  dry  up  they  burrow  into  the  wet  mud  and 
breathe  by  means  of  lungs  which  are  spongy  sacs  of  which 
the  air-bladder  of  other  fishes  is  a  degenerate  representative. 
As  we  shall  see,  they  resemble  in  this  respect  the  tadpoles 
and  some  adult  Amphibia  (frogs  and  salamanders).     The 
paired  fins  are  also  peculiar  in  structure,  having  an  elongate 
jointed  axis,  with  a  fringe  of  rays  along  its  length,  a  struc- 
ture almost  as  much  like  that  of  the  limbs  of  a  frog  as  that 
of  a  fish's  fin.     In  fact  the  Dipnoi  must  be  regarded  as  an 
ancestral  type,  an  ally  of  the  generalized  form  from  which 
Amphibia  and  bony  fishes  have  descended.     Only  four  liv- 
ing species  of  dipnoans  are  known,  but  great  numbers  of 
fossil  species  are  found  in  the  rocks. 

154.  The  bony  fishes   (Teleostei).— The  bony  fishes,  or 
Teleosts,  are  distinguished  by  the  bony  skeleton,  the  sym- 
metrical tail,  and  by  the  development  of  the  air-bladder  as 
a  more  or  less  completely  closed  sac,  useless  in  respiration. 


THE  FISHES  161 

Often  this  organ  is  altogether  wanting,  as  in  the  common 
mackerel.  About  ten  thousand  kinds  of  bony  fishes  are 
known.  The  species  swarm  in  every  sea,  lake,  or  river 
throughout  the  earth,  and  some  form  or  another  among 
them  is  familiar  to  every  boy  in  the  land.  These  fishes  are 
divided  into  about  two  hundred  families,  and  these  may  be 
arranged  in  fifteen  to  twenty  orders.  As  these  are  mostly 
distinguished  by  features  of  the  skeleton,  we  need  not  name 
them  here.  In  Jordan  and  Evermann's  Fishes  of  North  and 
Middle  America,  as  well  as  in  various  other  books,  the  stu- 
dent of  fishes  can  find  the  characters  by  which  orders  may 
be  distinguished. 

155.  Sturgeons  and  garpikes  (Ganoidea).— While  the  great 
majority  of  the  typical  fishes  possess  a  bony  skeleton,  there 
are  a  few  quaint  types— the  ganoid  fishes,  such  as  the  stur- 
geons (Fig.  101)  and  garpikes— in  which  it  is  cartilaginous  or 
partly  bony.  In  past  ages  these  were  probably  the  highest 
type  of  fishes,  and  from  their  fossil  remains  we  may  con- 
clude that  they  flourished  in  vast  numbers ;  but  at  present 
they  are  almost  extinct.  In  this  country  the  ganoids  are 
represented  by  several  species,  the  best  known  being  the 
sturgeons  which  inhabit  the  Great  Lakes,  the  Mississippi, 
and  its  tributaries ;  while  on  the  East  coast  the  common 
sturgeon  (Acipenser  sturio)  often  leaves  the  sea  and  ascends 
rivers.  They  are  the  largest  fishes  found  in  fresh  water, 
attaining  a  length  of  ten  or  twelve  feet,  and  a  weight  of 
five  hundred  pounds.  Their  food  consists  of  small  plants 
and  animals,  which  they  suck  in  through  their  tube-like 
mouth.  The  garpikes  live  in  the  larger  lakes  and  rivers 
throughout  the  East  and  Mississippi  Valley.  Their  bodies, 
from  three  to  ten  feet  in  length,  according  to  the  species, 
are  covered  with  comparatively  large  regularly  arranged 
square  scales,  and  the  upper  jaw  is  elongated  to  form  a 
kind  of  beak,  abundantly  supplied  with  teeth.  They  are 
carnivorous,  voracious  fishes,  working  great  havoc  among 
the  more  defenseless  food-fishes. 


THE  FISHES  163 

156.  The  catfishes. — Lowest  of  all  the  bony  fishes  we  may 
place  the  great  group  to  which  almost  all  fresh-water  fishes 
belong.     In  this  group  the  four  vertebrae  situated  next  the 
head  are  firmly  united,  and  by  means  of  certain  small  lever- 
like  bones  a  connection  is  formed  between  the  air-bladder 
and  the  ear  of  the  fish,  which  is  sunk  deep  in  the  skull. 
The   air-bladder  thus  becomes  a  sounding   organ  in  the 
function  of  hearing.     The  family  of  catfishes  possesses  this 
structure,  and  the  student  should  look  for  it  in  the  first  one 
he  catches.     The  catfishes  are  remarkable  for  the  long  feel- 
ers about  the  mouth,  with  which  they  pick  their  way  on  the 
bottom  of  a  pond.     There  are  many  kinds  the  world  over. 
The  small  ones  are  known  as  horned  pout  or  bullhead.     In 
these  the  dorsal  and  pectoral  fins  are  armed  each  with  a 
strong,  sharp  spine,  which  is  set  stiff  when  the  fish  is  dis- 
turbed, and  makes  them  very  troublesome  to  handle.     The 
catfishes  have  no  scales. 

157.  The  carp-like  fishes. — The  still  greater  carp  family 
includes  all  the  carp,  dace,  minnows,  and  chubs.     They 
have  the  air-bladder  joined  to  the  ear,  just  like  the  catfish, 
but  they  lack  the  long  feelers  and  the  fin  spines,  while  the 
soft  body  is  covered  with  scales,  and  there  are  no  teeth  in 
the  mouth.    In  the  throat  are  a  few  very  large  teeth,  which 
the  ingenious  boy  should  find.     In  the  sucker  family  these 
throat  teeth  are  like  the  teeth  of  a  comb,  and  the  mouth  is 
fitted  for  sucking  small  objects  on  the  river  bottom. 

158.  The  eels.— In  the  great  order  of  eels  the  body  is 
long  and  slim,  scaleless,  or  nearly  so,  with  no  ventral  fins. 
The  shoulder-girdle  has  slipped  back  from  the  head,  so  as 
to  leave  a  distinct  neck,  while  ordinary  fishes  have  none. 
Of  eels  there  are  very  many  kinds — some  large  and  fierce, 
some  small  as  an  earthworm ;  and  one  kind  comes  into  fresh 
water. 

159.  Herring  and  salmon. — In  the  great  order  which  in- 
cludes the  herring  and  salmon  the  vertebras  are  all  alike, 
the  ventral  fins  far  from  the  head,  and  the  scales  smooth  to 


164  ANIMAL  FORMS 

the  touch.  The  herring  and  shad  are  examples,  as  also  the 
salmon  and  trout.  Some  live  in  the  great  depths  of  the 
sea,  even  five  miles  below  the  surface.  These  are  very  soft 
in  body,  being  under  tremendous  pressure.  They  are  inky 
black — for  the  sea  at  that  depth  seems  black  as  ink — and 
most  of  them  have  luminous  spots  which  give  them  light 
in  the  darkness.  Some  species  have  the  forehead  luminous, 
like  the  headlight  of  an  engine.  Most  of  these  deep-sea 
fishes  are  very  voracious,  for  there  is  nothing  for  them  to 
feed  on  save  their  neighbors. 

160.  The  pike,  sticklebacks,  etc.— Several   small   orders 
stand  between  these  soft-rayed,  smooth-scaled  fishes  and 


Jfte.  108.— The  blindfish  and.  its  parentage.  A,  Dismal  Swamp  fish  (Chologaster 
atelvj),  the  ancestor  of  (B)  Agassiz's  cave  fish  (Chologaster  agassizi)  and  (C) 
cave  bJindfish  (Typhlichlhys subterraneus). 

the  form,  like  the  perch  and  bass,  which  has  many  spines  in 
the  dorsal  fin.  Among  these  transitional  forms  is  the  pike 
(Fig.  103) — long,  slender,  circumspect,  and  voracious,  lying 
in  wait  under  a  lily-pad ;  the  blindfish,  which  lost  its  eyes 
through  long  living  in  the  streams  of  the  great  caves ;  the 
stickleback,  small,  wiry,  malicious,  and  destructive,  steal- 
ing the  eggs  and  nibbling  the  fins  of  any  larger  fish ;  the 
sea-horse,  clinging  with  its  tail  head  downward  to  floating 


' 


166  ANIMAL  FORMS 

seaweed,  the  male  carrying  the  eggs  about  in  his  pocket 
until  they  hatch ;  the  mullet,  stupid,  blundering,  feeding 
on  minute  plants,  crushing  them  in  a  gizzard  like  that  of 
a  hen,  but  withal  having  soft  flesh,  good  for  the  table ;  the 
flying-fishes,  which  sail  through  the  air  with  great  swiftness 
to  escape  their  enemies. 

161.  The  spiny-rayed  fishes. — In  the  group  of  spiny- 
rayed  fishes  the  ventral  fins  are  brought  forward  and  joined 
to  the  shoulder-girdle.  The  scales  are  generally  rough  to 
the  touch,  and  the  head  is  usually  roughened  also.  There 
are  many  in  every  sea,  ranging  in  size  from  the  Everglade 
perch  of  Florida,  an  inch  long,  to  the  swordfish,  which  is 
thirty.  These  are  the  most  specialized,  the  most  fish-like 
of  all  the  fishes.  Leading  families  are  the  perch,  in  the 
fresh  waters,  the  common  yellow  perch,  familiar  to  all  boys 
in  the  Northeastern  States ;  the  darters,  which  are  dwarf 
perches,  beautifully  colored  and  gracefully  formed,  living 
on  the  bottoms  of  swift  rivers ;  the  sunfishes,  with  broad 
bodies  and  shining  scales,  thriving  and  nest-building  in 
the  quiet  eddies ;  the  sea-bass  of  many  kinds,  all  valued  for 
the  table ;  the  mackerel  tribe,  mostly  swimming  in  great 
schools  from  shore  to  shore.  After  these  come  the  multi- 
tude of  snappers,  grunts,  weakfishes,  bluefishes,  rose-fishes, 
valued  as  food.  Then  follow  the  gurnards,  with  bony 
heads;  the  sculpins,  with  heads  armed  with  thorns,  the 
small  ones  in  the  rivers  most  destructive  to  the  eggs  of 
trout ;  and  at  the  end  of  the  long  series  a  few  families  in 
which  the  spines  once  developed  are  lost  again,  and  the 
fins  have  only  soft  and  jointed  rays.  It  is  a  curious  law  of 
development  that  when  a  structure  is  once  highly  special- 
ized it  may  lose  its  usefulness,  at  which  point  degeneration 
at  once  sets  in.  Among  fishes  of  this  type  are  the  cod- 
fishes, with  spindle-shaped  bodies,  and  the  flounders,  with 
flat  bodies.  The  flounders  lie  on  the  sand  with  one  side 
down,  and  the  head  is  so  twisted  that  the  eyes  come  out  to- 
gether on  the  side  that  lies  uppermost.  This  side  is  col- 


168  ANIMAL  FORMS 

ored  like  the  bottom — sand  colored  or  brown  or  black — and 
the  under  side  is  white.  When  the  flounder  is  first  hatched, 
the  eyes  are  on  each  side  of  the  head,  and  the  animal 
swims  upright  in  the  water  like  other  fishes.  But  it  soon 
rests  011  the  bottom ;  it  turns  to  one  side,  and  as  the  body 
is  turned  over  the  lower  eye  begins  to  move  over  to  the 
other  side.  Finally,  we  may  close  the  series  with  the  an- 
glers (Fig.  105),  in  which  the  first  dorsal  spine  is  trans- 
formed into  a  sort  of  fishing-pole  with  a  bait  at  the  end, 
which  may  sometimes  serve  to  lure  the  little  fishes,  which  are 
soon  swallowed  when  once  in  reach  of  the  capacious  mouth. 

162.  Internal  anatomy.— A  few  fishes  are  vegetarians,  but 
the  greater  number  are  carnivorous.  Some  swallow  large 
quantities  of  sand  of  the  sea-bottom  and  absorb  from  it  the 
small  organisms  living  there.  Others  are  provided  with 
beaks  for  nipping  off  corals  and  tube-dwelling  worms.  Huge 
plate-like  teeth  enable  others  to  crush  mollusks,  sea-urchins, 
and  crabff,  and  many  are  adapted  for  preying  upon  other 
fishes.  /The  latter  are  often  able  to  escape,  owing  to  the 
presence  of  numerous  spines,  sometimes  supplied  with 
poison-glands ;  or  their  colors  are  protective,  and  a  vast 
number  of  devices  are  present  which  enable  them  with 
some  degree  of  surety  to  escape  their  enemies  and  capture 
food. 

Usually,  without  mastication,  the  food  passes  into  the 
digestive  tract  (Fig.  106),  which  in  the  main  resembles  that 
of  the  squirrel,  but  varies  considerably  according  to  the 
nature  of  the  food  it  is  required  to  absorb.  As  in  other 
animals,  it  is  usually  longer  in  the  vegetable  feeders.  In 
most  fishes  the  walls  of  the  canal  are  pushed  out  at  the 
junction  of  the  stomach  and  intestine,  to  form  numerous 
processes  like  so  many  glove-fingers  (the  pyloric  cceca,  Fig. 
106,  py.c.),  which  probably  serve  to  increase  the  absorptive 
surface.  The  same  result  is  obtained  in  other  ways,  chiefly 
by  numerous  folds  of  the  lining  of  the  canal. 

The  blood-system  is  much  more  complex  in  the  fishes 


THE  FISHES 


1P>9 


than  in  any  of  the  invertebrates.  It  also  differs  in  its  gen- 
eral plan  from  that  of  most  adult  vertebrates,  owing  to  the 
peculiar  method  of  respiration.  In  almost  every  case  the 


FIG.  105. — Angler  or  frogfish  (Lojrfiin*  piscatorius}.    One-tenth  natural  size.— After 
BASKETT. 

vessels  returning  from  all  parts  of  the  body  unite  into  one 
vein  leading  into  the  heart,  which  consists  of  only  one 
auricle  and  ventricle  (Fig.  106).  From  the  heart  the  blood 


170  ANIMAL  FORMS 

is  forced  through  the  gills,  with  all  their  delicate  filaments, 
and  now,  laden  with  oxygen  and  nutritious  substances  al- 
ready absorbed  from  the  coats  of  the  digestive  tract,  it 


Fie.  106.— Dissection  of  a  bony  fish,  the  tront  (Salmo).    a.U.,  air-bladder  :  an. 

opening;  aw.,  auricle;  gl.st.,  gills;  ffttl.,  esophagus;  int.,  intestine;  id.,  kidney ; 
lr.,  liver ;  Lor.,  ovary;  optJ.,  brain  ;  py.c.,  pyloric 'coeca  ;  gp.c..  spinal  cord  ;  ?])!., 
spleen  ;  */.,  stomach  ;  v.,  ventricle. 

travels  on  to  all  parts  of  the  body,  continually  unloading 
its  cargo  in  needy  districts  and  waste  matters  in  the  kid- 
neys before  returning  once  more  to  the  heart. 

163.  The  senses  of  fishes. — The  habits  of  fishes  indicate 
that  they  know  considerable  of  what  is  going  on  in  the 
outside  world,  and  their  well-developed  sense-organs  show 
the  degree  of  their  sensitiveness.  A  share  of  this  informa- 
tion comes  through  the  sense  of  touch,  which  is  distributed 
all  over  the  surface  of  the  body,  chiefly  in  the  more  ex- 
posed regions  sometimes  especially  provided  with  fleshy 
feelers,  like  those  on  the  chin  of  the  catfish. 

The  sense  of  smell  appears  to  be  fairly  developed,  as  is 
that  of  hearing ;  but  there  is  no  evidence  of  a  sense  of  taste. 
A  few  fishes  chew  their  food,  and  may  possibly  taste  it,  but 
there  are  others  that  swallow  it  whole,  and  in  all  there  are 
relatively  a  few  nerves  going  to  the  tongue  or  floor  of  the 
mouth. 


THE  FISHES  171 

The  eyes  of  most  fishes  are  highly  developed,  and  are  of 
the  greatest  use  at  all  times.  Exceptions  to  the  rule  are 
found  in  certain  species  which  live  in  caves  or  in  the  dark 
abysses  of  the  ocean.  In  some  of  these  the  eyes  have  dis- 
appeared almost  completely,  and  the  sense  of  touch  be- 
comes correspondingly  more  acute  ;  in  other  deep-sea  forms 
they  have  grown  to  a  large  size,  enabling  them  to  distin- 
guish objects  in  the  gloom,  like  the  owls  and  other  noc- 
turnal animals.  Embedded  in  the  skin  of  some  of  these 
deep-sea  fishes,  and  certain  nocturnal  ones,  are  peculiar 
spots,  composed  of  a  glandular  substance,  which  produces 
a  bright  glow  like  that  of  the  fireflies.  These  may  be  located 
on  the  head  or  arranged  in  patterns  over  various  parts  of 
the  body,  and  may  serve  to  light  the  fish  on  its  way  and 
enable  it  to  see  its  food  to  better  advantage,  or  it  may  act 
as  a  lure  to  many  fishes  that  become  victims  to  their  own 
curiosity.  In  those  fishes  which  are  active  most  of  the 
time  the  eyes  are  located  on  the  sides  of  the  head,  and  in 
those  which  remain  at  or  near  the  bottom  they  are  turned 
toward  the  top ;  in  every  case  where  they  can  be  used  to 
the  best  advantage. 

164.  Breeding  habits. — Among  fishes  the  egg-laying  time 
usually  comes  with  the  spring,  when  the  males  of  several 
species  become  more  resplendent,  and  sometimes  engage 
in  struggles  for  their  respective  mates.  In  others  this 
ceremony  is  performed  without  show  of  hostility.  Some 
make  nests,  while  others  lay  their  eggs  loosely  in  the  water. 

In  all  the  salmon  family  the  young  fishes  are  born  in 
the  colder  fresh-water  rivers,  and  later  make  their  way  into 
the  sea,  where  they  spend  the  greater  part  of  their  lives. 
When  the  time  comes  for  them  to  lay  their  eggs  they 
migrate  in  great  companies,  and  make  their  way  hundreds, 
perhaps  thousands,  of  miles  to  .the  rivers  in  which  they 
spent  their  youth.  Up  these  streams  they  rush  in  crowds, 
leaping  waterfalls  and  rapids,  and,  dashed  and  battered  on 
the  rocks,  many,  and  in  some  species  all,  die  from  injuries 


172  ANIMAL   FORMS 

or  exhaustion  after  the  breeding  season  is  passed.  The 
eggs,  like  those  of  the  chubs,  suckers,  sunfishes,  and  cat- 
fishes,  are  usually  buried  in  shallow  holes  in  the  sand,  and 
the  males  of  most  fishes  keep  a  faithful  watch  over  the 
young  until  they  are  able  to  live  in  safety.  In  some  of 
the  sticklebacks  and  several  marine  species  elaborate  nests 
are  composed  of  grass  or  seaweeds ;  some  of  the  catfishes 
carry  the  eggs  until  they  hatch  in  their  mouths  or  else  in 
folds  of  spongy  skin  on  the  under  side  of  the  body  ;  in  the 
pipefishes  and  sea-horses  a  slender  sac  along  the  lower  sur- 
face of  the  male  acts  as  a  brood-pouch,  in  which  the  female 
places  the  eggs  to  remain  until  developed ;  and  some  fishes, 
such  as  the  surf-fishes  and  a  number  of  the  sharks,  bring 
forth  their  young  alive.  On  the  other  hand,  the  young  of 
many  of  the  herrings,  salmon,  cod,  perch,  and  numerous 
other  fishes  are  abandoned  at  their  birth,  and  fall  a  prey  to 
many  animals,  even  their  parents  often  included. 

In  the  former  cases,  where  the  young  are  protected,  only 
a  relatively  few  eggs  are  produced :  where  they  are  aban- 
doned the  female  often  lays  many  millions.  In  every  case 
the  number  of  eggs  is  in  direct  relation  to  the  chances  the 
young  have  of  reaching  maturity,  a  few  out  of  each  brood 
surviving  to  perpetuate  the  race. 

165.  Development  and  past  history. — The  eggs  of  the 
higher  bony  fishes  are  usually  small  (one-tenth  to  one-third 
of  an  inch  in  diameter),  and  the  young  when  they  hatch 
are  accordingly  little ;  in  the  sharks  the  eggs  are  larger, 
the  size  of  a  hen's  egg  or  even  larger,  and  the  young  when 
born  are  relatively  large  and  powerful.  Thes%  differences, 
however,  do  not  greatly  affect  the  early  development,  for 
in  every  case  the  head  and  then  the  trunk  soon  become 
formed,  gills  arise,  the  nervous  system  appears,  which  is 
invariably  supported  by  a  skeleton  in  the  form  of  a  gristly 
rod — the  notochord.  In  the  lower  forms  of  fishes  this  per- 
sists throughout  life ;  but  in  the  sharks  and  skates  it  be- 
comes replaced  in  the  adult  by  another  and  higher  type  of 


THE  FISHES  173 

skeleton,  which  is  much  more  specialized  with  the  bony 
fishes. 

Those  who  study  the  fossils  on  the  rocks  tell  us  that 
the  first  fishes  were  very  simple,  and  many  believe  that 
their  skeleton,  like  that  of  the  little  growing  fish,  consisted 
only  of  a  notochord.  Many  of  these  old  forms  died  out 
long  ago,  while  others  gradually  changed  in  one  way  and 
another  to  adapt  themselves  to  their  surroundings,  the  con- 
stant need  of  adaptation  having  resulted  in  the  multitude 
of  present-day  types.  Some,  such  as  the  lamprey,  have 
probably  changed  relatively  only  to  a  slight  extent ;  others, 
like  the  sharks  and  skates,  are  much  more  altered;  and 
the  bony  fishes  are  far  from  their  original  low  estate, 
though  their  development  has  been  rather  toward  a  greater 
specialization  for  aquatic  life  than  an  advance  upward. 
The  little  fish  in  its  growth  from  the  egg  thus  repeats  the 
history  of  its  ancestral  development ;  but  as  though  in 
haste  to  reach  the  adult  condition,  it  omits  many  impor- 
tant details.  Moreover,  the  record  in  the  rocks  is  not 
complete,  and  we  have  many  things  yet  to  learn  of  the 
ancient  fishes  and  their  development  from  age  to  age  to 
the  present  day. 


CHAPTEK   XV 

THE    AMPHIBIANS 

IN  many  respects  the  amphibians — toads,  frogs,  and  sala- 
manders— resemble  the  fishes,  especially  the  lung-fishes 
(Dipnoi).  The  modern  amphibians  are  essentially  fishes 
in  their  early  life,  but  in  developing  legs  and  otherwise 
changing  their  bodily  form  they  become  adapted  for  a  life 
on  land  under  conditions  differing  from  those  of  the  fishes. 
Judging  from  this  class  of  facts,  we  may  assume  that  fish- 
like  ancestors,  by  the  development  of  the  lungs,  became 
fitted  for  a  life  on  land,  and  that  from  these  the  amphib- 
ians of  our  times  have  been  derived. 

166.  Development. — The  eggs  of  the  Amphibia  are  laid 
during  the  spring  months  in  fresh-water  streams  and  ponds. 
They  are  globular,  about  as  large  as  shot,  and  are  embedded 
in  a  gelatinous  envelope  (Fig.  107).  They  are  either  de- 
posited singly  or  in  clumps,  or  festooned  in  long  strings  over 
the  water-weeds.  During  the  next  few  days  development 
proceeds  rapidly  under  favorable  conditions,  resulting  in  an 
elongated  body  with  simple  head  and  tail.  In  this  condition 
they  are  hatched  as  tadpoles.  As  yet  they  are  blind  and 
mouthless,  but  lips  and  horny  jaws  soon  appear,  along  with 
highly  developed  eyes,  ears,  and  nose.  External  fluffy  gills 
arise  on  the  sides  of  the  head,  and  slits  form  in  the  walls  of 
the  throat,  between  which  gills  are  attached,  and  over  which 
folds  of  skin  develop,  as  in  the  fishes.  A  fin-fold  like  that 
of  the  lancelet  or  lamprey  appears  on  the  tail.  The  brain 
and  spinal  cord,  extending  along  the  line  of  the  back,  are 
supported  by  a  gristly  notochord,  and  complete  and  com- 
174 


THE  AMPHIBIANS  175 

plex  internal  organs  adapt  the  animal  to  a  free-swimming 
existence  for  days  to  come. 

The  t&dpole  is  now,  to  all  intents  and  purposes,  a  fish — 
a  fact  most  clearly  recognized  in  its  form,  method  of  loco- 


FIG.  107.— Metamorphosis  "of  the  toad.— Partly  after  GAGE,  from  Animal  Life. 

motion,  the  arrangement  of  the  gills,  and  the  general  plan 
of  the  circulatory  system. 

167.  Further  growth. — In  the  course  of  the  next  few 
weeks  hind  limbs  develop  beneath  the  skin,  through  which 
they  finally  protrude.  In  the  same  manner,  fore  limbs  arise 
at  a  later  date.  In  position  these  organs  are  like  the  paired 
fins  of  fishes,  but  they  are  intended  for  crawling  or  leaping 
on  land,  and  are  modified  in  accordance  with  this  need.  As 
in  the  higher  vertebrates,  the  limbs  develop  as  arms  and 
legs,  with  long  fingers  and  toes,  between  which  are  stretched 
webs  of  skin,  which  serve  in  swimming. 


176  ANIMAL   FORMS 

In  the  meantime  large  internal  changes  are  also  taking 
place.  The  wall  of  the  esophagus  has  gradually  pouched 
out  to  form  the  lungs.  They  are  richly  supplied  with  blood- 
vessels, closely  resembling  in  their  general  features  the 
lungs  of  the  lung-fishes.  The  animal  now  rises  to  the  sur- 
face occasionally  to  gulp  in  air,  and  it  also  continues  to 
breathe  by  means  of  gills.  At  this  stage  of  its  existence, 
therefore,  the  larva  is  amphibious  (two-living),  and  we  have 
the  interesting  example  of  an  animal  extracting  oxygen 
from  both  the  water  and  the  air.  The  diet  of  the  tadpole 
at  this  time  changes  from  vegetable  to  animal  substances, 
and  horny  teeth  give  way  to  the  small  teeth  of  the  frog, 
and  the  digestive  system  undergoes  an  entire  remodeling 
to  adapt  it  to  its  new  duties.  The  young  amphibian — 
whether  frog,  toad,  or  salamander — is  now  a  four-legged 
creature,  with  well-developed  head  and  tail,  with  lungs  and 
gills,  though  the  latter  are  usually  fast  disappearing,  and  is 
rapidly  assuming  those  characters  which  will  fit  it  for  a 
terrestrial  or  semiaquatic  existence. 

108.  The  salamanders. — The  changes  which  now  ensue  in 
such  a  larva  in  reaching  the  adult  condition  are  relatively 
slight  in  the  lower  salamanders.  The  external  gills  often 
persist  (Eig.  110),  the  lungs  are  also  functional,  and  the 
changes  are  largely  those  of  increase  of  size.  In  the  larger 
number  of  species  the  gills  disappear  more  or  less  com- 
pletely (Fig.  108),  such  species  often  abandoning  the  water 
for  homes  in  damp  soil  or  under  stones  and  logs,  returning 
to  it  only  when  the  time  comes  for  their  eggs  to  be  laid. 
The  limbs  are  always  relatively  weak,  never  supporting  the 
body  from  the  ground,  but  serving  in  a  clumsy  way  to  push 
it  from  place  to  place.  In  the  aquatic  forms  the  tail  con- 
tinues to  serve  as  a  swimming  organ.  In  some  species  the 
hind  legs  become  rudimentary,  or  even  entirely  lacking. 
A  still  further  modification  occurs  in  a  few  burrowing  spe- 
cies, which  move  by  wrigglings  of  the  body,  and  are  with- 
out either  pairs  of  legs. 


THE   AMPHIBIANS 


m 


In  geological  times  many  of  the  salamanders  were  of 
great  size,  several  feet  in  length,  and  some  were  enclosed 
in  an  armor  consisting  of  bony  plates.  All  now  living  have 
the  skin  naked,  and  with  the  exception  of  the  giant  species 
of  Japan,  three  feet  in  length,  and  a  few  similar  forms  in 
America,  the  modern  representatives  are  comparatively 


FIG.  108. — Blunt-nosed,  salamander  (Amblysloma  opacum).     Photograph  by  W.  H. 

FlSHBB. 

feeble  and  measure  their  length  by  inches.  Only  a  few,  on 
account  of  their  bright  colors,  are  particularly  attractive, 
while  the  others  are  usually  shunned  and  considered  re- 
pulsive, chiefly  because  of  their  supposed  poisonous  char- 
acter, though  in  reality  few  animals  are  more  harmless. 

169.  Tailless  forms. — In  the  frogs  and  toads  the  meta- 
morphosis which  the  young  undergo  is  almost  as  profound 
as  that  which  takes  place  with  the  insects.  The  gills,  to- 
gether with  their  blood-vessels,  disappear  completely.  The 
tail,  with  its  muscles,  nerve-supply,  and  skeleton,  is  ab- 
sorbed. The  cartilaginous  notochord  gives  way  to  a  jointed 
back-bone.  A  skull  is  developed ;  numerous  bones  form  in 
the  limbs,  affording  an  attachment  for  the  powerful  muscles 
which  make  the  toad,  and  especially  the  frog,  expert  swim- 


ITS  ANIMAL   FORMS 

mers  and  leapers,  and  thus  equipped  they  hereafter  lead  a 
wholly  terrestrial  or  seiniaquatic  life. 

170.  Distribution  and  common  forms. — All  the  Amphibia 
are  dependent  upon  moisture.  Almost  all  are  hatched  and 
developed  in  fresh  water,  and  those  which  leave  the  water 
return  to  it  during  the  breeding  season.  So  we  find  repre- 
sentatives of  the  group  all  over  the  world  having  much  the 
same  range  as  the  fresh- water  fishes.  The  great  majority 
of  the  salamanders  are  confined  to  the  northern  hemisphere, 
but  the  toads  and  frogs  are  almost  universally  distributed. 

Among  the  salamanders  in  this  country  only  a  relatively 
few  species  completely  retain  their  external  gills.  This  is 
the  case  with  sirens  and  mud-puppies  or  water-dogs  (Fig. 
110),  which  may  occasionally  be  seen  in  the  clear  waters 
of  our  lakes  and  rivers  crawling  slowly  about  in  search  of 
food,  and  every  now  and  then  rising  to  the  surface  to  gulp 
in  air.  The  remainder  lose  their  gills  more  or  less  com- 
pletely, and  usually  leave  the  water  for  damp  haunts  on 
land.  One  of  the  blunt-nosed  salamanders,  known  as  the 
tiger  salamander  (Amblystoma  tigrinuni),  is  found  in  moist 
localities  in  most  parts  of  the  United  States.  Besides  these 
are  numerous  small  species,  among  them  the  newts  (Die- 
myctylus],  ranging  widely  over  the  United  States,  living 
under  logs  and  stones  and  feeding  upon  the  small  insects 
and  worms  inhabiting  such  situations.  In  several  species 
of  salamanders  the  lungs  disappear  with  age,  and  respira- 
tion is  performed  solely  through  the  surface  of  the  skin. 

The  tailless  amphibians  are  much  more  abundant  and 
familiar  objects  than  the  salamanders,  and  from  the  open- 
ing of  spring  until  late  in  the  fall  they  are  met  with  on 
every  hand.  With  few  exceptions  the  frogs  live  in  or  about 
ponds  and  marshes,  in  which  they  obtain  protection  in 
troublous  times  and  from  which  they  derive  the  store  of 
worms  and  insects  that  serve  as  food.  On  the  other  hand, 
the  tree-frogs,  as  their  name  indicates,  usually  abandon  the 
water  and  repair  to  moist  situations  in  trees  and  other  vege- 


THE   AMPHIBIANS  1YO 

tatiou.  Their  shrill,  cricket-like  calls  are  often  heard  in 
the  summer.  The  fingers  and  toes  are  more  or  less  dilated 
into  disks  at  their  tips,  enabling  them  to  climb  with  con- 
siderable facility;  and  they  are  further  adapted  to  their 
surroundings  on  account  of  their  protective  colors.  The 
toads  undergo  their  metamorphosis  while  very  small,  and 
approach  only  the  water  at  the  breeding  season.  During 
the  day  they  remain  concealed  in  holes  and  crevices,  but  at 
the  approach  of  evening  come  out  in  search  of  food. 

171.  Means  of  defense.— The  food  of  the  members  of  this 
group  consists  chiefly  of  small  fishes,  insect  larvae,  snails, 
and  little  crustaceans,  which  are  swallowed  whole.     On  the 
other  hand,  many  Amphibia  prey  on  each  other,  while  most 
of  them  are  eagerly  sought  by  birds  and  fishes.     Some,  as 
the  toads,  stalk  their  food  only  during  the  night-time  or 
depend  upon  their  agility  to  escape  their  enemies.     Others 
are  colored  protectively,  the  markings  of  the  skin  resem- 
bling the  foliage  of  the  earth  upon  which  they  rest,  and  in 
some  species,  as  the  tree-toads,  this  color-pattern  changes 
as  the  animal  shifts  its  position.     A  few  species  are  most 
brilliantly  colored  with  red,  green,  yellow,  or  combinations 
of  these,  in  striking  contrast  to  their  surroundings.     They 
have  apparently  few  enemies,  possibly  because  of  an  un- 
pleasant odor  or  taste,  and  it  has  been  suggested  that  their 
gorgeous  tints  are  danger-signals,  warning  their  would-be 
captors  from  attempting  a  second  time  to  devour  them.   At 
the  same  time  it  is  well  known  that  the  somber-hued  toads 
emit  a  milky  secretion   from  the  warty  protuberance  of 
their  skin  which  is  intensely  bitter,  irritating  to  delicate 
skin,  and  poisonous  to  several  animals. 

172.  Skeleton. — As  in  all  vertebrates,  the  skeleton  of  the 
amphibian  first  arises  as  a  cartilaginous  rod,  the  notochord, 
which  is  afterward  replaced  by  a   jointed  back-bone,  to 
which  the  limbs  are  attached.     The  back-bone  is  anteriorly 
modified  into  a  flat,  usually  complex,  skull.     In  the  sala- 
manders the  number  of  vertebrae  is  sometimes  very  large, 


180 


ANIMAL  FORMS 


and  the  body  correspondingly  long  and  snake-like ;  but  in 
other  cases  parts  of  the  vertebrae  are  reduced  in  number, 
and  the  body  is  rather  short  and  thick.  In  the  frogs  and 
toads  this  reduction  reaches  its  culmination,  for  only  nine 
distinct  vertebrae  are  present,  the  tail  vertebrae,  correspond- 
ing to  those  of  the  salamanders,  being  represented  by  a 
rod-like  bone,  the  urostyle,  made  of  segments  grown  to- 
gether. 

173.  Digestive  and  other  systems.— In  its  main  characters 
the  digestive  tract  of  the  amphibian  (Fig.  109)  resembles 


bl. 


Ir. 


FIG.  109.— Dissection  of  toad  (Bnfo).  an.,  anal  opening;  a«.,  auricle;  U.,  bladder; 
duo.,  duodenum  ;  Ing.,  lung ;  Ir.,  liver;  pn.,  pancreas  ;  ret.,  rectum  ;  spl.,  spleen; 
St.,  stomach  ;  v.,  ventricle. 

that  of  the  fishes  and  the  squirrel.  The  mouth  is  usually 
large,  and  the  teeth  are  very  small,  as  in  the  frog  or  sala- 
mander, or  are  lacking  completely,  as  in  the  common  toad. 
In  many  salamanders  the  tongue,  like  that  of  a  fish,  is  fixed 
and  incapable  of  movement.  In  most  of  the  frogs  and 
toads  it  is  attached  to  the  front  of  the  mouth,  leaving  its 
hinder  portion  free,  and  capable  of  being  thrown  over  and 
outward  for  a  considerable  distance.  In  the  throat  region 
gill-clefts  may  persist,  but  they  usually  close  as  the  lungs 
reach  their  development.  The  succeeding  portions  of  the 
canal  are  comparatively  straight  in  the  elongated  forms,  or 


THE  AMPHIBIANS  181 

% 

more  or  less  coiled  in  the  shorter  species.  In  some  cases 
no  well-marked  stomach  exists,  but  ordinarily  the  different 
portions,  as  they  are  shown  in  Fig.  109,  are  well  denned. 

As  noted  above,  the  circulation  in  the  tadpole  is  the 
same  as  in  fishes,  then  lungs  arise,  and  for  a  time  respi- 
ration is  effected  both  by  gills  and  lungs,  and  the  cir- 
culation resembles  in  its  essential  points  that  of  the 
lung-fishes.  This  may  continue  throughout  life,  but  more 
frequently  the  gills  and  their  vessels  disappear,  and  the 
circulation  approaches  that  of  the  reptiles.  In  such  forms 
the  heart  consists  of  two  auricles  and  one  ventricle.  Into 
the  left  auricle  pours  the  pure  blood  from  the  lungs  ;  into 
the  right  the  impure  blood  from  the  body.  To  some 
extent  these  mix  as  they  are  forced  into  the  general  cir- 
culation by  the  single  ventricle.  The  amount  of  oxygen 
carried  is  therefore  smaller  than  in  the  higher  air-breathers, 
the  amount  of  energy  is  proportionately  less,  and  hence  it 
is  that  all  are  cold-blooded  and  of  comparatively  sluggish 
habits. 

In  some  sp'ecies  of  salamanders  the  lungs  may  also  dis- 
appear, and  breathing  is  carried  on  by  the  skin,  as  it  is  to 
a  certain  extent  in  all  amphibians.  In  the  frogs  and  toads 
lungs  are  invariably  present,  and  vocal  organs  are  situated 
at  the  opening  of"  the  windpipe  in  the  throat.  These  pro- 
duce the  characteristic  croaking  or  shrilling,  which  in  many 
species  are  intensified  through  the  agency  of  one  or  two 
large  sacs  communicating  with  the  mouth-cavity. 

Although  the  brain  is  small  in  the  amphibians,  it  is 
more  complex  in  several  respects  than  it  is  in  fishes. 
The  eyes  are  also  usually  well  developed,  but  in  some  of 
the  cave  and  burrowing  salamanders  they  are  concealed 
beneath  the  skin,  and  are  rudimentary.  The  ear  varies 
considerably  in  complexity  in  the  different  species,  but  in 
the  possession  of  semicircular  canals  and  labyrinth  resem- 
bles that  of  the  fishes.  In  the  frogs  and  toads,  as  one  may 
readily  discover,  the  drum  or  tympanum  is  external,  ap- 


182 


ANIMAL  FOKMS 


pearing  as  a  smooth  circular  area  behind  the  eye.  Organs 
of  touch,  smell,  and  taste  are  likewise  developed  in  varying 
degree  of  perfection. 

174.  Breeding-habits. — While  the  great  majority  of  am- 
phibians mate  in  the  spring  and  deposit  their  eggs  in  the 
water,  often  to  the  accompaniments  of  croakings  and  pip- 
ings almost  deafening  in  intensity,  several  species,  for 
various  reasons,  have  adopted  different  methods.  Some  of 
the  salamanders  bring  forth  young  alive,  and  several  species 
of  toads  and  frogs  are  known  in  which  the  young  are  cared 
for  by  the  parent  until  their  metamorphosis  is  complete. 
In  one  of  the  European  toads  (Alytes)  the  male  winds 
the  strings  of  eggs  about  his  body  until  the  tadpoles  are 


FIG.  110.— Salamanders.  The 
axolotl  (the  larva  of  Am- 
blystoma  tigrimtm}  and 
the  newt  (Diemyctyhts  to- 
rosits). 


ready  to  hatch  ;  and  in  a  few  species  of  tree-toads  the  eggs 
are  stored  in  a  great  pouch  on  the  back  of  the  parent  until 
the  early  stages  of  growth  are  over.  In  the  Surinam  toad 
of  South  America  the  eggs  are  placed  by  the  male  on  the 
back  of  the  female,  and  each  sinks  into  a  cavity  in  the 
spongy  skin.  Here  they  pass  through  the  tadpole  stage 
without  the  usual  attendant  dangers,  and  emerge  with  the 
form  of  the  adult. 


THE  AMPHIBIANS  183 

Sunlight  and  warmth  are  apparent  necessities  for  speedy 
development.  Tadpoles  kept  in  captivity  where  the  con- 
ditions are  generally  unfavorable  may  require  years  to  as- 
sume the  adult  form.  As  mentioned  above,  the  tiger  sala- 
mander (AmUystoma  tigrinum)  occurs  in  most  parts  of  the 
United  States  and  Mexico.  In  the  East  this  species  drops  its 
gills  in  early  life  as  other  salamanders  do,  and  assumes  the 
adult  form,  but  in  the  cold  water  of  high  mountain  lakes, 
in  Colorado  and  neighboring  States,  it  may  never  become 
adult,  always  remaining  as  in  Fig.  110.  This  peculiar  form 
is  locally  known  as  axolotl.  In  this  condition  it  breeds.  It 
is  thus  one  of  the  very  few  examples  of  animals  whose  un- 
developed larvaB  are  able  to  produce  their  kind.  Owing  to 
this  trait  it  was  at  first  considered  a  distinct  species,  and 
many  years  elapsed  before  its  relationship  to  the  true  adult 
form  was  discovered. 


CHAPTER  XVI 

THE    REPTILES 

175.  General  characteristics. — In  all  the  reptiles  the  gen- 
eral shape  of  the  body,  and  to  some  extent  the  internal 
plan,  is  not  materially  different  from  that  seen  among  the 
amphibians.  In  spite  of  external  resemblance  the  actual 
relationship  is  not  very  close.  It  appears  to  be  true  that 
ages  ago  the  ancestors  of  the  modern  reptiles  were  aquatic 
animals,  possibly  somewhat  similar  to  some  of  the  sala- 
manders; but  they  have  become  greatly  changed,  and 
are  now,  strictly  speaking,  land  animals.  At  no  time  in 
their  development  after  leaving  the  egg  do  we  find  them 
living  in  the  water  and  breathing  by  gills.  Some  species, 
such  as  the  turtles,  lead  aquatic  or  semiaquatic  lives,  but 
the  modifications  which  fit  them  for  such  an  existence 
render  them  only  slightly  different  from  their  land-inhabit- 
ing relatives.  The  skin  bears  overlapping  scales  or  horny 
plates,  united  edge  to  edge,  as  in  the  turtles,  enabling  them 
to  withstand  the  attacks  of  enemies  and  the  effects  of  heat 
and  dryness.  Indeed,  it  is  when  heat  is  greatest  that  rep- 
tiles are  most  active.  In  no  other  class  of  vertebrates,  and 
very  few  invertebrates,  do  normal  activities  of  the  body 
appear  to  be  so  directly  dependent  upon  external  warmth. 
In  the  presence  of  cold  they  rapidly  grow  sluggish,  and 
sink  into  a  dormant  state. 

As  in  the  case  of  all  animals,  habits  depend  upon 
structure,  and  accordingly  among  the  reptiles  we  find 
many  remarkable  modifications,  enabling  them  to  lead 
184 


THE  REPTILES 


185 


widely  different  lives.      Nevertheless  all  are  constructed 
upon  much  the  same  plan. 

176.  The  lizards  (Sauria).— As  in  the  amphibians,  es- 
pecially the  salamanders,  the  body  (Fig.  Ill)  consists  of 
a  relatively  small  head  united  by  a  neck  to  the  trunks, 


FIG.  111. — Common  lizard  or  swift  (ScelojxMits  tindulatus).    Photograph  by  \V.  II. 
FISHER. 

which,  in  turn,  passes  insensibly  into  a  tail,  usually  of  con- 
siderable length.  Two  pairs  of  limbs  are  almost  always 
present,  and  these  exhibit  the  same  skeletal  structure  as 
in  the  amphibians ;  but  in  their  construction,  as  in  the 
other  divisions  of  the  body,  we  note  a  grace  of  propor- 
tion and  muscular  development  which  enable  the  lizards 
to  execute  their  movements  with  an  almost  lightning-like 
rapidity.  The  mouth  is  large  and  slit-like,  well  armed  with 
teeth,  and  the  eyes  and  ears  are  keen.  Scales  of  various 


186  ANIMAL  FORMS 

forms  and  sizes,  always  of  definite  arrangement,  cover  the 
body.  The  scales  are  always  colored,  in  some  species  as 
brilliantly  as  the  feathers  of  birds,  and  usually  harmonize 
with  the  surroundings  of  the  animal,  enabling  it  to  escape 
the  attacks  of  its  many  enemies.  Altogether  the  lizards 
are  a  very  attractive  group  of  animals.  As  in  the  salaman- 
ders, the  vertebral  column  is  usually  of  considerable  length, 
but  it  too  presents  a  lighter  appearance  and  a  greater  flexi- 
bility. Slender  ribs  are  present,  and  a  breast-bone  and  the 
girdles  which  support  the  limbs.  Although  more  ossified 
than  in  the  amphibians,  the  skull  still  continues  to  be  com- 
posed here  and  there  of  cartilage.  The  roof  also  is  yet 
incomplete,  but  with  the  firm  plates  on  the  surface  of  the 
head  ample  protection  is  afforded  the  small  brain  under- 
neath. As  above  mentioned,  the  limbs  are  slender  and 
insufficient  to  support  the  body,  which  accordingly  rests 
upon  the  ground,  and  by  its  wrigglings  and  the  pushing  of 
the  limbs  is  borne  from  place  to  place.  It  will  be  recalled 
that  some  of  the  salamanders  living  in  subterranean  haunts 
and  burrowing  in  the  soil  have  no  need  of  limbs,  and  the 
latter  have  accordingly  disappeared.  This  condition  is 
paralleled  by  certain  species  of  lizards.  The  blindworms 
(which  are  neither  blind  nor  worms,  but  true  lizards,  though 
snake-like  in  appearance)  are  devoid  of  limbs,  as  are  also 
the  "  glass-snakes."  In  some  species  the  hinder  pair  arise 
in  early  life,  but  they  remain  small,  and  ultimately  disap- 
pear. In  almost  all  lizards  the  tail  is  very  brittle,  breaking 
at  a  slight  touch.  In  such  case  the  lost  member  will  grow 
again  after  a  time. 

177.  The  snakes  (Serpentes).— The  snakes  are  character- 
ized by  a  cylindrical,  generally  greatly  elongated  body,  in 
which  the  divisions  into  head,  neck,  trunk,  and  tail  are  not 
sharply  defined.  As  we  have  seen,  this  is  also  true  of  cer- 
tain lizards,  but  the  naturalist  finds  no  difficulty  in  detecting 
the  differences  between  them.  Another  peculiarity  of  the 
snakes  is  in  the  great  freedom  of  movement  of  the  bones 


THE  REPTILES 


187 


not  concerned  with  the  protection  of  the  brain.  In  the 
reptiles  the  lower  jaw  does  not  unite  directly  with  the 
skull,  as  in  the  higher  animals,  but  to  an  intermediate 
bone,  the  quadrate,  which  is  attached  to  the  skull.  In  the 
snakes  these  unions  are  made  by  means  of  elastic  liga- 
ments. The  two  halves  of  the  lower  jaw  are  also  held 


FIG.  112.—  Blacksnake  (B 


iistrictor).    Photograph  by  W.  H.  FISHER. 


together  by  a  similar  band,  so  that  the  entire  palate  and 
lower  jaw  are  loosely  hung  together.  This  enables  the 
snake  to  distend  its  mouth  and  throat  to  an  extraordinary 
degree,  and  to  swallow  frogs  and  toads  but  slightly  smaller 
than  itself.  Where  the  prey  is  of  relatively  small  size,  the 
halves  of  the  lower  jaw  alternate  with  each  other  in  pulling 
backward,  thus  drawing  the  food  down  the  throat.  The 
food  is  never  masticated.  The  teeth  are  usually  small  and 
recurved,  and  serve  only  to  hold  the  food  until  it  may  be 
swallowed.  The  latter  process  is  facilitated  by  the  copious 
secretion  of  the  salivary  glands,  which  become  very  active 
at  this  time. 

A  further  character  of  the  snakes  is  the  absence  exter- 


188  ANIMAL  FORMS 

nally  of  any  trace  of  limbs.  However,  in  some  of  the 
pythons  and  boas  hind  limbs  are  present  in  the  form  of 
small  groups  of  bones  embedded  beneath  the  skin  and  ter- 
minating in  a  claw.  There  thus  appears  to  be  no  doubt 
that  the  ancestors  of  the  modern  snakes  were  four-footed, 
lizard-like  creatures,  which  have  assumed  the  present  form 
in  response  to  the  necessity  of  adaptation  to  new  conditions. 

More  than  any  other  order  of  vertebrates  do  the  snakes 
deserve  the  name  of  creeping  things,  and  yet  their  method 
of  locomotion  enables  them  to  crawl  and  swim  with  a  ra- 
pidity equal  to  that  of  many  of  the  more  highly  developed 
animals.  This  depends  chiefly  upon  certain  peculiarities 
of  the  skeleton,  which  consists  merely  of  a  skull,  vertebral 
column,  and  ribs.  The  vertebrae,  usually  two  or  three  hun- 
dred in  number,  are  united  together  by  ball-and-socket 
joints,  and  each  attaches  by  similar  joints  a  pair  of  slender 
ribs.  These  in  turn  are  attached  to  the  broad  outer  plates 
upon  which  the  body  rests,  and  the  whole  system  is  operated 
by  a  powerful  set  of  muscles.  Upon  the  contraction  of  the 
muscles  the  ventral  plates  are  made  to  strike  backward 
upon  the  ground  or  other  rough  surface,  which  drives  the 
body  forward.  Also,  the  ribs  may  be  made  to  move  back- 
ward and  forward,  and  the  snake  thus  progresses  like  a 
centiped  or  "thousand-legs." 

178.  The  turtles  (Chelonia). — In  many  respects  the  tur- 
tles are  the  most  highly  modified  of  all  the  reptiles.  The 
body  (Fig.  113)  is  short  and  wide  and  enclosed  in  a  shell  or 
heavy  armor,  consisting  of  an  upper  portion,  the  carapace, 
and  a  flat  ventral  plate,  the  plastron.  The  shape  of  the 
carapace  varies  greatly  from  a  low,  flat  shield  to  a  highly 
vaulted  dome,  remaining  cartilaginous  throughout  life,  as 
in  the  soft-shelled  turtles,  or  becoming  bony  and  of  great 
strength.  These  two  portions  of  the  shell  form  a  box-like 
armor,  through  whose  openings  the  head,  tail,  and  limbs 
may  be  extended.  The  latter  organs  are  superficially  unlike 
those  of  any  other  order  of  animals.  The  head  is  generally 


THE  REPTILES  189 

thick-set  and  muscular,  and  provided  with  horny  jaws 
entirely  destitute  of  teeth,  like  those  of  the  birds.  The 
limbs  also  are  usually  short  and  thick  and  variously  shaped, 
and  adapted  for  aquatic  or  terrestrial  locomotion.  The 
number  of  vertebrae  in  the  body  and  tail  are  relatively  few, 
and  the  thick  and  heavy  body  is  devoid  of  the  elements  of 
grace  and  agility  of  movement  characteristic  of  the  other 
reptiles.  On  the  other  hand,  the  former  enjoy  a  freedom 
from  the  attacks  of  enemies  not  accorded  to  animals  in 
general. 

At  first  sight  the  appearance  of  a  turtle  does  not  indi- 
cate a  close  relationship  to  the  other  reptiles,  but  a  more 


FIG.  113.— Box-turtle  (Terrapene  Carolina). 

careful  examination,  and  especially  of  their  development, 
discloses  a  remarkable  resemblance.  The  head,  tail,  and 
limbs  are  essentially  similar  to  those  of  the  lizards,  but  in 
the  trunk  region  peculiar  modifications  have  taken  place. 
The  ribs  at  first  separate,  as  in  other  animals,  flatten 
greatly,  and  unite  with  a  number  of  bones  embedded  in 
the  skin,  thus  forming  one  great  plate  overlying  the  back 
of  the  animal.  About  the  circumference  of  the  shield 
other  dermal  or  skin-bones  are  added,  which  increase  the 
area  of  the  carapace,  and  at  the  same  time  still  others  have 


190  AXIMAL  FORMS 

arisen  and  united  on  the  ventral  surface  to  form  the  plas- 
tron. In  this  process  the  shoulder-  and  hip-girdles  which 
attach  the  limbs  come  to  be  withdrawn  into  the  body,  and 
we  have  the  curious  example  of  an  animal  enclosed  within 
its  back-bone  and  ribs.  This  is  even  more  the  case  with 
the  box-turtles  (Fig.  113),  common  in  the  eastern  United 
States,  whose  ventral  plate  is  hinged  so  that  after  the 
limbs,  head,  and  tail  have  been  withdrawn  it  may  be  made 
to  act  like  a  lid  to  completely  enclose  the  fleshy  parts  of 
the  body. 

Scales  and  horny  plates  are  present,  as  in  other  reptiles, 
the  former  covering  all  parts  of  the  body  except  the  cara- 
pace and  plastron,  which  support  the  plates.  In  nearly  all 
species  the  latter  are  of  considerable  size,  and  in  the  tor- 
toise-shell turtles  are  valuable  articles  of  commerce.  They 
also  are  sculptured  in  a  fashion  characteristic  of  each  spe- 
cies, and  may,  like  the  colors  of  other  animals,  render  them 
more  like  their  surroundings,  and  consequently  incon- 
spicuous. 

179.  Crocodiles  and  alligators  (Crocodilia).— The  alligators 
(Fig.  114)  and  crocodiles  are  much  more  complex  in  struc- 
ture than  the  lizards,  though  their  general  form  is  much  the 
same.  The  body  is  covered  with  an  armor  of  thick  bony 
shields  and  horny  scales.  These,  along  the  median  line,  are 
keeled,  and  extending  along  the  length  of  the  laterally  com- 
pressed tail  form  an  efficient  swimming  organ  and  rudder. 
The  mouth  is  of  large  size,  and  is  bounteously  supplied  with 
large  conical  teeth,  which  are  set  in  sockets  in  the  jaw,  and 
not  fused  with  it,  as  in  many  of  the  lizards.  The  nose  and 
ears  may  be  closed  by  valves  to  prevent  the  entrance  of 
water,  and  a  similar  structure  blocks  its  passage  beyond 
the  throat  while  the  mouth  is  open.  When  large  animals, 
such  as  hogs  or  calves,  are  captured  as  they  come  to  drink, 
these  devices  enable  the  alligator  or  crocodile  to  sink  with 
them  to  the  bottom  and  hold  them  until  drowned.  The 
limbs,  short  and  powerful,  are  efficient  organs  of  locomo- 


THE   REPTILES  191 

tion  on  land,  and  together  with  the  general  shape  of  the 
body,  are  also  well  adapted  for  swimming. 


FIG.  114.— Alligator  (Alligator  mississippiensis). 

180.  Distribution  of  the  lizards. — In  a  general  way  the 
number  of  reptiles  is  greatest  where  the  temperature  is 
highest.  The  tropics  therefore  abound  in  species,  often 
of  large  size,  and  usually  of  bright  coloration.  As  one 
travels  northward  the  numbers  rapidly  diminish,  their  size 
is  smaller,  and  the  tints  less  pronounced.  In  all  probability 
not  less  than  four  thousand  known  reptiles  exist,  whose 
haunts  are  of  the  most  varied  description. 

In  ^North  America  the  lizards  are  almost  exclusively 
confined  to  the  southern  portions,  only  a  very  few  species 
extending  up  to  the  fortieth  parallel.  Among  these  the 
skinks  (Eumeces]  are  most  widely  distributed.  The  blue- 
tailed  skink  is  probably  the  most  familiar,  a  small  lizard 
eight  or  ten  inches  in  length,  dark  green  with  yellowish 
streaks  and  a  bright-blue  tail.  On  sunny  days  it  may 
sometimes  be  seen  darting  about  on  the  bark  of  trees  in 
search  of  insects,  upon  which  it  feeds. 

One  of  the  most  familiar  lizards  in  this  country  is  the 
"glass-snake,"  found  burrowing  in  the  drier  soil  of  the 
southern  half  of  the  United  States  east  of  the  Mississippi. 


192 


ANIMAL   FORMS 


Both  pairs  of  limbs  are  absent,  but  by  wriggling  movements 
of  the  body  this  lizard  is  able  to  force  its  way  through  light 
soil  with  considerable  rapidity.  It  is  a  matter  of  some 
difficulty  to  secure  entire  specimens,  for  with  other  than 
the  gentlest  handling  the  tail  severs  its  connection  with 
the  body,  as  the  vertebra  in  this  portion  are  extremely 
brittle.  This  peculiarity,  together  with  its  shape,  has  given 
it  the  popular  name  of  glass-snake.  Many  species  of  liz- 
ards will  thus  detach  the  tail,  a  habit  which  is  a  means  of 
protection,  enabling  the  animal  to  scamper  away  into  a 
place  of  safety  while  its  enemy  is  concerning  itself  with 
the  detached  member.  Later  on  a  new  tail  develops, 
though  usually  of  a  less  symmetrical  form. 

181.  Horned  toads. — The  horned  toads  (Phrynosoma)  are 
lizards  peculiar  to   the   hot,  sandy  deserts  and  plains  of 


FIG.  115. — Gila  monster  (Heloderma  susjxctum).    One-third  natural  size. 

Mexico  and  the  western  United  States.  The  body  is  com- 
paratively broad  and  flat,  almost  toad-like,  and  is  covered 
with  scales  and  spines  of  brownish  and  dusky  tint,  so  like 
dried  sticks  and  cactus  spines  in  form  and  color  as  to  ren- 
der them  difficult  of  detection.  In  captivity  they  readily 


THE   REPTILES  193 

adapt  themselves  to  their  new  surroundings,  become  tame, 
and  feast  on  flies,  ants,  and  other  insects,  which  they  cap- 
ture by  the  aid  of  their  long  tongue.  The  horned  toads 
are  perfectly  harmless  creatures,  but  when  irritated  some- 
times perform  the  remarkable  feat  of  spurting  a  stream  of 
blood  from  the  eye  toward  the  intruding  object  for  a  dis- 
tance of  several  inches.  This  has  been  regarded  by  some 
as  a  zoological  fable  ;  but  there  are  many  who  have  watched 
the  horned  toad  in  its  natural  state  and  in  captivity,  and 
they  assure  us  that  it  is  a  fact. 

In  the  hot  deserts  of  Arizona  and  Sonora  is  another 
peculiar  species  of  lizard  known  as  the  Gila  monster  (Hclo- 
derma)  (Fig.  115),  having  the  distinction  of  being  the  only 
poisonous  lizard  known.  Further  protection  is  afforded 
by  bony  tubercles  on  the  head  and  by  scales  over  the 
remainder  of  the  body,  all  of  which  are  colored  brown  or 
various  shades  of  yellow,  giving  the  animal  a  peculiar 
streaked  and  blotched  appearance. 

182.  Distribution  of  the  snakes. — The  snakes  are  much 
more  common  than  the  lizards.  All  over  the  United  States 
one  meets  with  them,  especially  the  garter-  or  water-snakes. 
Of  less  wide  distribution  are  the  black-,  grass-,  and  milk- 
snakes,  and  a  number  of  less  known  species,  all  of  which 
are  perfectly  harmless  and  often  make  interesting  pets. 
Some  of  them  when  cornered  show  considerable  temper, 
flatten  the  head  and  hiss  violently,  and  imitate  poisonous 
forms,  but  venomous  snakes  are  comparatively  few  in  num- 
ber in  northern  and  eastern  United  States.  In  the  south- 
ern portions  of  the  country  they  become  more  abundant. 
Along  the  streams  and  in  the  swamps  the  copperheads,  and 
especially  the  water-moccasins,  often  lie  in  wait  for  frogs 
and  fish.  Both  these  species  are  especially  dreaded,  as  they 
strike  without  giving  any  warning  sound,  but  the  name 
and  bad  reputation  of  the  moccasin  is  often,  especially  in 
the  'South,  transferred  to  perfectly  harmless  water-snakes. 
On  higher  ground  are  the  rattlesnakes  (Crotalus),  once 


194 


ANIMAL   FORMS 


abundant  but  now  in  many  regions  well-nigh  exterminated. 
In  these  species  the  tail  terminates  in  a  series  of  horny 


rings  that  produce  a  buzzing  sound  like  that  of  the  locust 
when  the  tail  is  rapidly  vibrated. 

183.  Distribution  of  the  turtles.— The  turtles  are  perhaps 
somewhat  less  dependent  upon  warmth  than  other  reptiles, 
yet  they  too  delight  to  bask  in  the  sunshine,  and  soon  grow 
sluggish  in  its  absence.  In  all  our  fresh-water  streams  and 
ponds  they  are  familiar  objects,  and  several  species  extend 
up  into  Canada.  Among  the  turtles  the  soft  shell,  the 
painted  and  the  snapping  turtles  have  the  widest  distri- 
bution, scarcely  a  good-sized  stream  or  pond  from  the  Gulf 
of  Mexico  to  Canada,  and  even  farther  north,  being  without 
one  or  more  representatives.  All  are  carnivorous  and  vora- 
cious, and  the  snapping  turtles  are  especially  ferocious,  and 
"for  their  size  are  the  strongest  of  reptiles."  In  the  woods 
and  meadows  the  wood-tortoise  and  box-turtles  are  occa- 


THE  REPTILES 


195 


sionally  met  with,  and  at  sea  several  turtles  exist,  some  of 
them  of  great  size.  Among  these  is  the  leather-turtle, 
found  in  the  warmer  waters  of  the  Atlantic,  lazily  floating 
at  the  surface  or  actively  engaged  in  capturing  food.  They 
attain  a  length  of  from  six  to  eight  feet,  and  a  weight  of 
over  a  thousand  pounds,  and  are  sometimes  captured  for 
food  when  they  come  ashore  to  bury  their  eggs  in  the  sand. 
By  this  same  method  the  loggerheads,  the  hawkbills,  and 
the  common  green  turtles  are  also  captured  in  consider- 
able numbers.  These  are  of  smaller  size,  and  the  second 
named  is  of  considerable  value,  as  the  horny  plates  cover- 


FIG.  117. — Hawkbill  turtle  (Eretmochelys  imbricata). 

ing  the  shell  furnish  the  tortoise-shell  of  commerce.  These 
plates  are  removed  after  the  animal  is  killed,  by  soaking 
in  warm  water  or  by  the  application  of  heat. 

184.  Food  and  digestive  system. — Some  reptiles,  among 
which  are  a  number  of  species  of  lizards  and  the  box-  and 
green  turtles,  are  vegetarians,  but  the  great  majority  are 


196  ANIMAL   FORMS 

carnivorous,  and  usually  very  voracious.  The  lizards  espe- 
cially devour  large  quantities  of  insects  and  snails,  together 
with  small  fishes  and  frogs.  The  latter  figure  largely  in 
the  turtle's  bill  of  fare,  and  in  that  of  the  snakes,  which 
also  capture  birds  and  mammals.  On  the  other  hand,  many 
of  the  reptiles  prey  upon  one  another ;  and  they  are  the 
favorite  food  of  hawks  and  owls  and  numerous  water-birds, 
of  skunks  and  weasels  and  many  other  animals,  which  look 
for  them  continually.  Many  of  the  turtles,  owing  to  their 
protective  armor,  and  the  snakes  because  of  their  poison- 
ous bite  or  great  size  and  strength,  are  more  or  less  ex- 
empt, but  this  is  not  true  of  their  eggs  and  young.  The 
smaller  species  depend  upon  keenness  of  sense,  agility,  and 
inconspicuous  tints.  These  latter  may  undergo  changes 
according  to  the  character  of  the  surroundings,  but  usually 
only  to  a  slight  extent.  The  chameleons  of  the  tropics 
and  a  similarly  colored  green  lizard  on  the  pine-trees  in 
the  Southern  States  are  able  to  change  with  great  rapidity 
from  green,  through  various  shades,  to  brown. 

185.  Respiration  and  circulation. — While  still  in  the  egg 
the  young  lizard  develops  rudimentary  gills,  and  thus  bears 


nntl    I  II 

'(rbh  ned    Inc '  ^  duff-MMM.  M. 

'Wj 

extna.-. 


ndcw  sts&^j^jjgjm 
7,      OJL^-- : 


FIG.  118.— Dissection  of  lizard  (Sceloporus).  an.,  anal  opening  ;  au.,  auricle  ;  crb.h., 
brain  ;  coec.,  intestine  ;  kd.,  kidney  ;  Ling.,  left  lung ;  lr.,  liver ;  pn.,  pancreas  ; 
sp.c.,  spinal  cord  ;  spl.,  spleen  ;  st..  stomach  ;  v.,  ventricle  of  heart. 


evidence  to  the  fact  that  its  distant  ancestors  were  aquatic  ; 
but  before  hatching  they  disappear,  and  lungs  arise,  which 


THE   REPTILES  197 

remain  functional  throughout  life.  Corresponding  to  the 
shape  of  the  body,  these  are  usually  much  elongated  and 
ordinarily  paired  (Fig.  118,  Ling.}.  The  snakes  are  peculiar 
in  having  the  left  lung  rudimentary  or  even  lacking  com- 
pletely, while  the  right  one  becomes  greatly  elongated  and 
extends  far  back  into  the  body.  In  nearly  all  the  reptiles 
the  amount  of  oxygen  brought  into  the  lungs  is  relatively 
large  and  the  activity  of  the  animal  is  proportionately 
great.  The  circulation  of  reptiles  shows  an  advance  be- 
yond that  of  the  Amphibia.  As  in  the  latter,  there  are 
two  distinct  auricles ;  but  the  chief  difference  arises  from 
the  fact  that  the  ventricle  is  more  or  less  divided  by  a  par- 
tition which  to  a  considerable  degree  prevents  the  blood 
returning  from  the  lungs  from  mixing  with  the  impure 
blood  as  it  returns  from  its  journey  over  the  body.  In  the 
crocodiles  and  alligators  the  partition  is  complete,  and  the 
circulation  thus  approaches  close  to  that  of  the  higher 
animals. 

186.  Hibernation. — Attention  has  already  been  called  to 
the  fact  that  reptiles  are  very  susceptible  to  cold,  rapidly 
growing  less  active  as  the  temperature  lowers.     When  win- 
ter comes  on  they  seek  protected  spots,  and  either  alone 
or  grouped  together  hibernate.     The  various  activities  of 
the  body  during  this  period  are  at  very  low  ebb.     The  blood 
barely    circulates,  breathing    is  imperceptible,   and   stiff 
and  insensible  to  the  world  about  them  they  remain  until 
the  warmth  again  stirs   them  to  their  former  activity. 
Some  of  our  common  turtles  must  also  pass  a  somewhat 
similar  sleep  while  embedded  far  down  in  the  mud  during 
the  disappearance  of  the  ponds  in  summer.     At  such  times 
no  food  is  taken,  but  owing  to  their  loss  in  weight  it  is 
probable  that  a  slow  consumption  of  the.  body  supplies  the 
small  amount  of  necessary  energy. 

187.  Nervous  system  and  sense-organs. — At  first  sight  one 
is  struck  with  the  small  size  of  the  brain  of  fishes,  Am- 
phibia, and  reptiles.     Their  intelligence  likewise  is  at  low 


198  ANIMAL   FORMS 

ebb.  Almost  all  the  movements  and  operations  of  the  body 
appear  to  be  carried  on  by  the  animal  with  little  apparent 
thought.  Their  acts,  like  most  of  the  animals  below  them, 
are  said  to  be  instinctive  ;  yet  they  are  sufficiently  well  done 
to  enable  the  animal  to  procure  its  food,  avoid  its  enemies, 
and  lead  a  successful  life.  As  is  true  of  other  animals,  the 
ability  of  the  reptile  to  cope  with  its  surroundings  depends 
to  a  great  extent  upon  the  keenness  of  one  or  all  of  its  or- 
gans of  special  sense.  In  the  reptiles  the  sense  of  sight  is 
perhaps  sharpest,  but  there  is  considerable  variation  in  this 
respect.  Eyelids  are  present  in  all  except  the  snakes,  to- 
gether with  a  third,  known  as  the  nictitating  membrane,  a 
thin,  transparent  fold  located  at  the  inner  angle  of  the  eye, 
over  which  it  is  drawn  with  great  rapidity.  In  the  snakes 
eyelids  are  absent,  giving  the  eye  its  characteristic  stare. 
Furthermore,  their  sense  of  sight,  except  in  a  few  tree-dwell- 
ing species,  appears  to  be  defective,  the  majority  depending 
largely  upon  the  sense  of  touch. 

In  all  the  vertebrates  a  very  peculiar  organ  known 
as  the  pineal  gland  or  eye  is  situated  on  the  roof  of  the 
brain.  In  several  lizards  its  position  is  indicated  by  a  trans- 
parent area  in  one  of  the  plates  of  the  head,  and  by  an 
opening  in  the  bones  of  the  roof  of  the  skull.  In  young 
reptiles,  and  especially  in  one  of  the  New  Zealand  lizards 
(Hatteria,  Fig.  119),  its  resemblance  to  an  eye  is  decidedly 
striking.  Lens,  retina,  pigment,  cornea,  are  all  present 
much  as  they  are  in  some  of  the  snails,  but  they  finally 
degenerate  more  or  less  as  the  animal  reaches  maturity. 
It  is  a  general  belief  that  it  represents  the  remnant  of  an 
organ  of  sight,  a  third  eye,  which  looked  out  through  the 
roof  of  the  skull  in  some  of  the  ancient  vertebrates. 

With  the  possible  exception  of  the  few  species  of  reptiles 
which  produce  sounds,  probably  to  attract  their  mate,  the 
sense  of  hearing  is  not  particularly  well  developed.  The 
senses  of  smell  and  taste  are  also  comparatively  feeble.  The 
latter  sense  is  located  in  the  tongue,  which  is  also  popularly 


THE   REPTILES  199 

supposed  to  serve  for  the  purpose  of  defense,  and  that  it  is 
in  someway  related  to  the  poison-glands.  This,  however, 
is  an  error.  The  tongue  is  used  primarily  as  an  organ  of 


FJG.  110.—  Tnatera  (Sphenodon  punctatus). 

touch,  and  in  snakes  especially  it  is  almost  continually 
darted  in  and  out  to  determine  the  character  of  the  animal's 
surroundings. 

188.  Egg-laying. — The  eggs  of  the  reptiles  are  relatively 
large  and  enclosed  in  a  shell  like  a  bird's  egg,  the  shell, 
however,  being  leathery  rather  than  made  of  lime.  These 
are  deposited  in  some  warm  situation,  and  generally  left  to 
themselves  to  hatch.  Under  stones,  logs,  and  leaves,  or 
buried  lightly  in  the  soil,  are  the  positions  most  frequently 
chosen  by  the  lizards  and  snakes.  The  turtles  almost  inva- 
riably select  the  warm  sand  at  the  edge  of  the  water,  and 
after  scooping  a  hole  lay  several  perfectly  spherical  eggs, 
usually  at  night.  The  alligators  lay  upward  of  a  hundred 
eggs  about  the  size  of  those  of  a  goose,  and  guard  them 
jealously  until  and  even  after  they  hatch.  On  the  other 
hand,  the  young  of  many  lizards  and  snakes  are  born  alive, 
the  eggs  being  hatched  within  the  body. 

Many  reptiles  are  surprisingly  slow  in  attaining  maturity, 
and  live  to  an  age  attained  by  few  other  animals.  It  is  a 
well-known  fact  that  turtles  live  fully  a  hundred  years,  and 
14 


200  ANIMAL  FORMS 

probably  the  same  is  true  of  the  crocodiles  and  alligators 
and  some  of  the  larger  snakes.  Their  enemies  are  few,  and 
death  usually  results  when  the  natural  course  is  run. 

Throughout  life  all  reptiles  periodically  shed  their  skin, 
as  birds  do  their  feathers  and  mammals  their  fur.  In  the 
snakes  and  some  of  the  lizards  the  skin  at  the  lips  loosens, 
and  the  animal  gradually  slips  out  of  its  old  slough,  bright 
and  glossy  in  the  new  one  which  previously  developed.  In 
the  others  the  old  skin  hangs  on  in  tatters,  gradually  com- 
ing away  as  they  scamper  through  the  grass. 


CHAPTEE  XVII 

THE    BIRDS 

189.  Characteristics. — Birds  form  one  of  the  most  sharp- 
ly defined  classes  in  the  animal  kingdom,  and  the  variations 
among  the  different  species  are  relatively  small.  "The 
ostrich  or  emu  and  the  raven,  for  example,  which  may  be 
said  to  stand  at  opposite  ends  of  the  series,  present  no  such 
anatomical  differences  as  may  be  found  between  a  common 
lizard  and  a  chameleon,  or  between  a  turtle  and  a  tortoise," 
and  these  we  know  to  be  relatively  slight. 

In  many  respects  the  birds  resemble  the  reptiles,  and 
long  ago  in  the  world's  history  the  relationship  was  much 
closer  than  now,  as  we  know  from  certain  fossil  remains  in 
this  country  and  in  Europe.  One  of  the  earliest  of  these 
fossil  birds,  that  of  the  Archaeopteryx,  is  a  most  remarkable 
combination  of  bird  and  lizard.  Unlike  any  modern  bird, 
the  jaws  were  provided  with  many  conical  reptile-like  teeth. 
The  wings  were  rather  small,  and  the  fingers,  tipped  with 
claws,  were  distinct,  not  grown  together,  as  in  modern  birds. 
The  tail  was  as  long  as  the  body,  and  many-jointed,  like  a 
lizard's,  each  vertebra  carrying  two  long  feathers.  The 
bird  was  about  the  size  of  a  crow,  and  it  probably  could 
not  fly  far.  Other  ancient  types  have  been  discovered — 
principally  sea-birds — many  of  which  existed  when  the 
Pacific  extended  over  the  region  now  occupied  by  the 
Eocky  Mountains.  These  were  all  of  the  same  generalized 
type,  intermediate  between  reptile  and  bird.  This  fact 
leads  us  to  the  belief  that  birds  descended  from  reptilian 

201 


202  ANIMAL  FORMS 

ancestors,  and  in  becoming  more  perfectly  adapted  for  an 
aerial  life  have  developed  into  our  modern  forms. 

In  the  modern  birds  the  most  important  peculiarities, 
those  which  separate  them  from  all  other  animals,  are 
correlated  with  the  power  of  flight.  The  body  is  spindle- 
shaped,  for  readily  cleaving  the  air.  The  fore  limbs  serve 
as  wings.  The  hind  limbs,  supporting  the  weight  of  the 
body  from  the  ground,  are  usually  well  developed.  A  series 
of  air-chambers  usually  exists  in  powerful  fliers.  This 
serves  a  purpose  analogous  to  that  of  the  air-bladder  of  a 
fish,  giving  buoyancy.  But  the  most  characteristic  mark 
of  a  bird,  as  above  stated,  is  its  feathers,  universally  present 
and  never  found  outside  the  class.  Like  the  scales  of 
lizards,  and  probably  derived  from  similar  structures,  thej 
are  of  different  forms,  and  serve  a  variety  of  purposes. 
The  larger  ones,  with  powerful  shafts,  and  forming  the  tail, 
act  as  a  rudder.  Those  of  the  wings  give  great  expanse 
with  but  little  increase  in  weight,  and  are  so  constructed 
that  upon  the  down-stroke  they  offer  great  resistance  to 
the  air,  and  push  the  bird  forward,  while  in  the  reverse 
direction  the  air  slips  through  them  readily.  In  flight 
these  movements  of  the  wing  may  be  too  rapid  for  us  to 
follow,  as  in  the  humming-birds,  though  they  are  usually 
much  slower,  two  to  five  hundred  a  minute  in  many  power- 
ful fliers,  such  as  the  ducks,  and  frequently  long-continued 
enough  to  carry  them  many  hundreds  of  miles  at  a  single 
flight.  The  remaining  feathers  are  soft  and  downy,  giving 
roundness  to  the  body  and  enabling  it  to  cleave  the  air  with 
greater  ease,  and,  being  poor  conductors  of  heat,  they  aid  in 
keeping  the  body  at  the  high  temperature  characteristic  of 
birds.  In  most  birds  the  body  is  not  uniformly  clothed  in 
feathers.  Xaked  spaces,  usually  hidden,  intervene  between 
the  feather  tracts,  and  on  the  feet  and  toes  scales  exist. 

190.  Molting. — As  we  all  know,  the  growth  of  feathers, 
unlike  that  of  hair  and  nails,  is  limited,  and  after  they  have 
become  faded  and  worn  out  they  are  shed,  and  new  ones 


THE   BIRDS  203 

arise  to  take  their  place.  This  process  of  molting  is 
usually  accomplished  gradually,  without  diminishing  the 
powers  of  flight ;  but  in  the  ducks  and  some  other  birds  all 
the  wing-  and  tail-feathers  drop  out  simultaneously,  leaving 
the  bird  to  escape  its  enemies  by  swimming  and  diving. 
The  mol ting-process  usually  takes  place  in  the  fall,  after 
the  nesting  and  care  for  the  young  is  over,  and  often  when 
the  need  for  a  heavy  winter  coat  commences  to  be  felt. 
Many  birds  also  don  what  are  called  courting  colors,  ruffs, 
crests,  and  highly  colored  patches,  in  the  spring,  previous 
to  the  mating  season,  doubtless  for  the  purpose  of  attract- 
ing or  impressing  their  mates.  In  other  cases  the  change 
appears  to  be  related  to  the  bird's  surroundings.  A  most 
beautiful  example  of  this  is  the  ptarmigans — grouse-like 
birds  living  far  to  the  north.  During  winter  they  are  per- 
fectly white  and  are  almost  invisible  against  the  snow ;  but 
in  the  spring,  as  the  snow  disappears,  the  white  feathers 
gradually  fall  out  and  new  ones  arise.  The  latter  so  har- 
monize "with  the  lichen-colored  stones  among  which  it 
delights  to  sit,  that  a  person  may  walk  through  a  flock  of 
them  without  seeing  a  single  bird." 

There  are  also  numerous  birds,  chiefly  those  that  go  in 
flocks,  which  possess  what  are  known  as  color-calls  or  recog- 
nition-marks. These  may  consist  of  various  conspicuous 
spots  or  blotches  on  different  parts  of  the  head  or  trunk, 
such  as  we  see  in  the  yellowhammer  or  meadow-lark ;  or 
one  or  more  feathers  of  the  wings  or  tail  may  be  strikingly 
colored,  as  in  many  sparrows  and  warblers.  During  the 
time  the  bird  remains  at  rest  these  usually  are  concealed 
under  neighboring  feathers,  but  during  flight  they  are 
strikingly  displayed.  It  may  possibly  be  true,  as  many 
have  urged,  that  these  color-signals  are  for  the  purpose 
of  enabling  various  members  of  the  flock  to  readily  follow 
their  leader ;  but  this  and  many  other  interesting  questions 
regarding  the  color  of  birds  and  other  animals  have  not  yet 
received  final  answers. 


204:  ANIMAL  FORMS 

In  very  many  animals,  fishes  as  well  as  birds,  the  tints 
on  the  under  side  of  the  body  are  usually  relatively  light 
colored,  shading  gradually  into  a  darker  tint  above.  This 
is  in  all  probability  a  protective  device,  as  was  recently 
shown  by  Mr.  A.  H.  Thayer,  an  American  artist.  His  ex- 
periments show  that  the  light  from  above  renders  the  back 
less  dark,  and  that  the  shadow  beneath  is  neutralized  by 
the  light  color.  The  bird  thus  appears  uniformly  lighted, 
and  this  effect,  together  with  streaks  and  blotches,  renders 
them  invisible  at  surprisingly  short  distances. 

191.  Skeleton. — Turning  now  to  the  internal  organization 
of  birds,  we  find  many  points  in  common  with  other  verte- 
brates, especially  the  reptiles,  but  many  interesting  modifi- 
cations are  also  present  that  adapt  them  for  flying  and  for 
collecting  their  food.  According  to  the  nature  of  the  food, 
the  beak  may  have  a  great  variety  of  forms.  The  skull  may 
be  thick  and  heavy,  or  thin  and  fragile,  but  these  are  mat- 
ters of  proportion  of  the  various  parts  possessed  by  all 
birds.  The  neck  also  is  of  differing  length  ;  but  it  is  in  the 
trunk  region  that  the  greatest  changes  have  arisen,  as  we 
may  see  in  any  of  our  ordinary  birds.  For  example,  the 
vertebrae  of  this  part  of  the  body  are  more  or  less  fused 
together  into  rigid  framework,  to  which  are  attached  the 
ribs  that  in  turn  unite  with  the  breast-bone.  In  the  fliers 
the  latter  bears  a  vertical  plate  or  keel,  to  which  the  great 
muscles  that  move  the  wings  are  attached.  The  tail  con- 
sists, like  that  of  the  old-fashioned  birds,  of  several  verte- 
brae, but  these  are  of  small  size  and  fused  together  into  a 
little  knob  that  supports  the  tail-feathers.  The  fore  limbs 
are  used  for  flight,  but  there  are  the  same  bones  that  exist 
in  the  fore  limbs  of  other  vertebrates — one  for  the  upper 
arm,  two  for  the  lower,  a  thumb  carrying  a  few  feathers, 
and  known  as  the  bastard  wing,  and  indications  of  several 
bones  that  form  the  hand.  In  the  hind  limb  the  resem- 
blance is  equally  apparent,  though  its  different  parts  are 
of  relatively  large  size  to  support  the  body.  It  is  interest- 


THE  BIRDS  205 

ing  to  note  that  the  knee  has  been  drawn  far  up  into  the 
body,  and  that  the  joint  above  the  foot  is  in  reality  the 
ankle. 

We  thus  see  that  the  bird's  skeleton  presents  the  same 
general  plan  as  that  of  the  lizard,  for  example  ;  but  in  order 
to  combine  the  elements  of  strength,  lightness,  and  com- 
pactness essential  to  successful  flight,  it  has  been  necessary 
to  remodel  it  to  a  considerable  degree. 

192.  Other  internal  structures. — The  lungs  of  birds  con- 
sist of  two  dark-red  organs  buried  in  the  spaces  between  the 
ribs  along  the  back.  Each  communicates  with  extensive 
thin- walled  air-sacs  extending  into  the  space  between  the 


intnal. 


FIG.  120. — Anatomy  of  a  bird,  au.,  auricle  ;  cbl.  and  crb.h.,  cerebellum  and  cerebral 
hemispheres  (divisions  of  the  brain) ;  duo.,  intestine  (with  portion  removed) ; 
giz.,  gizzard;  kd.,  kidney;  r.lng.,  lung;  tr.,  trachea  or  windpipe;  vent.,  ven- 
tricle. 

various  organs,  and  in  many  birds  of  flight  they  even  extend 
into  the  bones  of  the  body,  and  thus  decrease  their  weight. 
"  The  enormous  importance  of  this  feature  to  creatures 
destined  to  inhabit  the  air  will  be  readily  understood  when 
we  learn  that  a  bird  with  a  specific  gravity  of  1.30  may 
have  this  reduced  to  only  1.05  by  pumping  itself  full  of  air." 
As  we  know,  air  is  taken  into  the  body  in  order  that  the 
oxygen  it  contains  may  combine  with  the  tissues  of  the 
body  to  liberate  the  energy  necessary  for  the  work  of  its 


206  ANIMAL  FORMS 

life.  The  deeper  and  more  frequent  the  breathing  the 
greater  the  amount  of  energy  produced.  Birds  habitually 
breathe  deeper  breaths  than  other  animals.  The  air  pass- 
ing into  the  body  traverses  the  entire  extent  of  the  lung 
on  its  way  back  to  the  air-sacs,  with  the  result  that  large 
quantities  of  oxygen  are  taken  into  the  body.  This  is  dis- 
tributed by  a  circulatory  system  of  a  more  highly  developed 
type  than  in  any  of  the  preceding  groups  of  animals.  The 
ventricles  of  the  heart  no  longer  communicate  with  each 
other,  and  the  pure  and  impure  blood  never  mingle.  Fur- 
thermore, the  beating  of  the  heart  is  comparatively  rapid, 
rushing  the  oxygen  as  fast  as  it  enters  the  blood  to  all  por- 
tions of  the  body.  The  result  is  that  everywhere  heat  is 
being  generated,  so  necessary  to  life  and  activity. 

In  the  lower  animals  no  special  means  are  employed  to 
husband  the  energy  thus  produced,  but  in  the  birds  the 
body  is  jacketed  in  a  non-conducting  coat  of  feathers  which 
prevents  its  dissipation.  For  this  and  other  reasons  the 
birds,  summer  and  winter,  maintain  an  even  and  relatively 
high  temperature  (102°-110°).  Like  the  mammals,  birds 
are  warm-blooded  animals,  full  of  energy,  restlessly  active 
to  an  extent  realized  in  few  of  the  cold-blooded  animals. 

193.  Digestive  system. — This  life,  at  high  pressure,  de- 
mands a  relatively  large  amount  of  food  to  make  good  the 
losses  due  to  oxidation.  The  appetites  of  some  growing 
birds  is  only  satiated  after  a  daily  meal  equal  to  from  one 
to  three  times  their  own  weight,  and  after  reaching  adult 
size  the  amount  of  daily  food  required  is  probably  not  less 
than  one-sixth  their  weight.  The  nature  of  the  food  is 
exceedingly  varied,  and  the  digestive  tract  and  certain  ac- 
cessory structures  are  obviously  modified  in  accordance 
with  it.  The  beak,  always  devoid  of  teeth  in  the  living 
form,  varies  extremely  according  to  the  work  it  must  per- 
form. The  same  is  true  of  the  tongue,  and  many  correlated 
modifications  exist  in  the  digestive  apparatus.  In  the 
birds  of  prey  and  the  larger  seed-eating  species,  such  as  the 


THE  BIRDS  207 

pigeons  and  the  domestic  fowls,  the  esophagus  dilates  into 
a  crop,  in  which  the  food  is  stored  and  softened  before  being 
acted  upon  by  the  gizzard.  The  latter  is  the  stomach,  pro- 
vided with  muscular  walls,  especially  powerful  in  the  seed- 
eaters,  and  with  an  internal  corrugated  and  horny  lining 
which,  in  the  absence  of  teeth,  serves  to  crush  the  food.  In 
some  species,  such  as  the  domestic  fowls  and  the  pigeons, 
this  process  is  aided  by  the  grinding  action  of  pebbles 
swallowed  along  with  the  food.  The  remaining  portions, 
with  pancreas  and  liver,  vary  chiefly  in  length,  and  are 
sufficiently  shown  in  Fig.  120  to  require  no  further  descrip- 
tion. 

194.  Nesting-habits.— A  few  birds,  such  as  the  ostriches 
and  terns,  merely  scoop  a  hollow  in  the  earth,  and  make  no 
further  pretense  of  constructing  a  nest.  On  the  other 
hand,  some  birds,  such  as  the  humming-birds  and  pewees, 
build  wonderful  creations  of  moss,  lichens,  and  spider-webs, 
lining  it  with  down,  and  concealing  it  so  skilfully  that 
they  are  not  often  found.  Every  bird  has  its  own  particular 
ideas  as  to  the  fitness  of  its  own  nest,  and  the  results  are 
remarkably  different,  and  form  an  interesting  feature  in 
studying  the  habits  of  birds.  Usually  the  female  takes 
upon  herself  the  choice  of  the  nest  and  its  construction ; 
but  these  duties  are  in  some  species  shared  by  the  male. 
After  the  eggs  are  laid,  the  male  may  also  aid  in  their 
incubation,  or  may  carry  food  to  the  female.  In  other 
species— for  example,  the  pigeons  and  many  sea-birds — the 
parents  take  turns  in  sitting  upon  the  eggs  and  in  the  sub- 
sequent care  of  the  young.  Finally,  there  are  certain  birds, 
such  as  the  cuckoo  and  cowbirds,  which  take  advantage  of 
the  industry  of  other  species  and  deposit  an  egg  or  two  in 
the  nests  of  the  latter.  All  the  work  of  incubation  and 
care  of  the  young  is  assumed  by  the  foster-parents,  which 
sometimes  neglect  their  own  offspring  in  their  desperate 
attempts  to  satisfy  the  appetites  of  the  rapidly  growing  and 
unwelcome  guests. 


208  ANIMAL  FORMS 

The  eggs  of  birds  are  relatively  large,  and  are  often 
delicately  colored.  In  some  species  the  blotches  and  streaks 
of  different  shades  are  probably  protective,  as  in  the  plovers 
and  sandpipers,  whose  eggs  blend  perfectly  with  their  sur- 
roundings, but  many  other  cases  exist  not  subject  to  such 
an  explanation. 

The  young  require  a  high  degree  of  heat  for  their  devel- 
opment, and  this  is  usually  supplied  by  the  parent.  In  a 
very  general  way  the  length  of  sitting,  or  incubation,  is 
proportional  to  the  size  of  the  egg,  being  from  eleven  to 
fourteen  days  in  the  smaller  species,  to  seven  or  eight  weeks 
in  the  ostriches.  Before  hatching,  a  sharp  spine  develops 
on  the  beak,  and  with  this  the  young  bird  breaks  its  way 
through  the  shell.  Among  the  quails,  pheasants,  plovers, 
and  many  other  species,  the  young  are  born  with  a  covering 
of  feathers,  wide-open  eyes,  and  the  ability  to  follow  their 
parents  or  to  make  their  own  way  in  the  world.  Such 
nestlings  are  said  to  be  precocial,  in  distinction  to  the  dltrical 
young  of  the  more  highly  specialized  species,  such  as  the 
sparrows,  woodpeckers,  doves,  birds  of  prey,  and  their  allies, 
which  are  born  helpless  and  depend  for  a  considerable  time 
on  the  parents  for  support. 

Some  of  the  owls,  crows,  woodpeckers,  sparrows,  quails, 
etc.,  remain  in  the  same  localities  where  they  are  bred. 
They  are  resident  birds.  The  greater  number,  at  the  ap- 
proach of  winter,  migrate  toward  the  southern  warmer 
climes,  some  species  traveling  in  great  flocks,  by  day  or 
night,  and  often  at  immense  heights.  In  some  cases  this 
movement  appears  to  be  directly  related  to  the  food-supply  ; 
but  there  are  many  apparent  exceptions  to  such  a  theory, 
and  it  is  possible  that  many  birds  migrate  for  other  reasons. 
Certain  species  migrate  thousands  of  miles,  along  fairly 
definite  routes,  the  young,  sometimes  at  least,  guided  by 
the  parents,  which  in  turn  appear  to  remember  certain 
landmarks  observed  the  year  before.  Sea-birds,  in  their 
journeys  northward  or  southward,  keep  alongshore,  occa- 


THE  BIRDS  .    209 

sionally  veering  in  to  get  their  bearings  or  to  rest,  espe- 
cially in  the  presence  of  fogs. 

195.  Classification. — Most  zoologists  make  two  primary 
divisions  of  the  living  types  of  birds — those  like  the  ostrich 
with  flat  breast-bones,  and  the  other  the  ordinary  birds,  in 
which  the  breast-bone  has  a  strong  keel  for  the  attachment 
of  the  powerful  muscles  used  in  flight.     This  distinction  is 
not  of  high  importance,  but  we  may  use  it  as  a  convenience 
in  the  description  of  a  few  typical  forms  belonging  to  sev- 
eral orders  into  which  these  two  divisions  are  subdivided. 

196.  The  ostriches,  etc.  (Ratitae). — From    specimens  in- 
troduced or  from  pictures  we  are  doubtless  familiar  with 
the  ostriches  and  with  some  of  their  relatives.    The  African 
ostrich  (Struthio  camelus,  Fig.  121)  is  the  largest  of  living 
birds,  attaining  a  height  of  over  seven  feet,  and  is  further 
characterized  by  a  naked  head  and  neck,  two  toes,  and 
fluffy,  plume-like  feathers  over  parts  of  the  body.     They 
are  natives  of  the  plains  and  deserts  of  Africa,  where  they 
travel  in  companies,  several  hens  accompanying  the  male. 
When  alarmed,  they  usually  escape  by  running  with  a  swift- 
ness greater  than  that  of  the  horse,  but  if  cornered  they 
defend  themselves  with   great   vigor  by  means   of   their 
powerful  legs  and  beaks.     Their  food  consists  of  insects, 
leaves,  and  grass,  to  which  is  added  sand  and  stones  for 
grinding  the  food,  as  in  the  domestic  fowl.     The  American 
ostriches  or  rheas,  are  smaller  ostrich-like  birds,  living  on 
the  plains  of  South  America.     Their  habits  are  essentially 
the  same  as  those  of  the  African  species. 

197.  The  loons,  grebes,  and  auks  (Pygopodes).— The  birds 
in  this  and  some  of  the  following  orders  are  aquatic  in 
their  habits.     All  have  broad,  boat-like  bodies,  which,  with 
the  thick  covering  of  oily  feathers,  enables  them  to  float 
without  effort.     The  legs  are  usually  placed  far  back  on 
the  body— a  most  favorable  place  for  swimming,  but  it  ren- 
ders such  birds  extremely  awkward  on  land.      The  grebes 
are  preeminently  water-birds.   The  pied-billed  grebe  or  dab- 


Hindus).    Photograph  by  WIL- 


IAM  GKAUAM. 


THE   BIRDS  211 

chick  (Podilymbuspodiceps),  for  example,  found  abundantly 
on  the  larger  lakes  and  streams  throughout  the  United 
States,  captures  its  food,  sleeps,  and  breeds  without  leaving 
the  water.  The  loons  living  in  the  same  situations  as  the 
dabchick  are  also  remarkable  swimmers  and  divers.  Of 
the  three  species  found  in  this  country,  the  common  loon 
or  diver  (  Garia  imber)  attains  a  length  of  three  feet,  and  is 
otherwise  distinguished  by  its  black  plumage,  mottled  and 
barred  with  white,  which  is  also  the  color  of  the  under 
parts.  The  auks,  murres  (see  frontispiece),  and  puffins  are 
marine,  and,  like  their  inland  relatives,  are  expert  swim- 
mers and  divers,  strong  fliers,  and  spend  much  of  their 
time  on  the  open  sea.  During  the  breeding-season  they 
assemble  in  vast  numbers  on  rugged  cliffs  along  the  shore, 
and  lay  their  eggs  on  the  bare  rock  or  in  rudely  constructed 
nests. 

198.  The  gulls,  terns,  petrels,  and  albatrosses  (Longi- 
pennes). — The  birds  belonging  to  this  group  are  among  the 
most  abundant  along  the  seacoast,  and  several  species  make 
their  way  inland,  where  they  often  breed.  All  are  char- 
acterized by  long,  pointed  wings  and  pigeon  or  swallow-like 
bodies,  which  are  carried  horizontally  as  the  bird  waddles 
along  when  ashore.  Many  are  excellent  swimmers  and 
powerful  fliers,  especially  the  petrels  and  albatrosses,  which 
sometimes  travel  hundreds  of  miles  at  a  single  flight. 

The  gulls  are  abundantly  represented  along  our  coasts, 
where  they  frequently  associate  in  companies,  usually  rest- 
ing lightly  on  the  surface  of  the  water,  or  wheeling  lazily 
through  the  air  on  the  lookout  for  food.  The  terns  are 
of  lighter  build  than  the  gulls  and  are  more  coastwise  in 
their  habits,  and  are  further  distinguished  by  plunging  like 
a  kingfisher  for  the  fishes  on  which  they  live.  Both  the 
gulls  and  terns  breed  in  colonies,  every  available  spot  over 
acres  of  territory  being  occupied  by  their  nests,  which  are 
usually  built  of  grass  and  weeds  placed  on  the  ground. 

The  petrels  and  albatrosses  are  at  home  on  the  high 


212 


ANIMAL  FORMS 


seas,  rarely  coining  ashore  except  at  the  breeding-season. 
Some  species  of  the  former  are  abundant  oif  our  shores? 
especially  the  stormy  petrel  (Procellaria  pelagica)  or  Mother 
Carey's  chickens  ( Oceanites  oceanicus),  which  are  often  seen 
winging  their  tireless  flight  in  the  wake  of  ocean  vessels. 
Among  the  dozen  or  so  albatrosses  few  reach  our  shores. 
The  wandering  albatross  (Diomedea  exulans),  celebrated  in 
story  and  as  the  largest  sea-bird  (fourteen  feet  between  the 
tips  of  its  outstretched  wings),  is  an  inhabitant  of  the 
southern  hemisphere,  and  only  rarely  extends  its  journeys 
to  more  northern  regions. 

199.  Cormorants  and  pelicans  (Steganopodes). — The  cor- 
morants and  pelicans  are  comparatively  large  water-birds 


FIG.  122.— White  pelicans  (P.  erythrorhynchus)  and  whoopiug-crane  (Grus  ameri- 
cana).    Photograph  by  W.  K.  FISHER. 

usually  abundant  along  the  seashore  and  in  many  sections 
of  the  United  States.     The  cormorants  or  shags  are  glossy 


THE  BIRDS  213 

black  in  color,  with  hooked  bills,  long  necks,  and  short 
wings,  which  give  them  a  duck-like  flight.  The  much 
larger  pelicans  (Fig.  122)  are  at  once  distinguished  by  long 
bills,  from  which  is  suspended  a  capacious  membranous  sac. 
All  these  birds  are  sociable  in  their  habits,  breeding,  roost- 
ing, and  fishing  in  great  flocks.  Their  food  consists  of 
fishes,  which  the  shags  pursue  under  water  and  capture  in 
their  hooked  beaks ;  while  the  pelicans,  diving  from  a  con- 
siderable height  or  swimming  rapidly  on  the  surface,  use 
their  pouches  as  dip-nets.  The  nests,  usually  built  of  sea- 
weed or  of  sticks,  are  placed  on  rocky  cliffs  or  on  the 
ground  in  less  elevated  places. 

200.  Ducks,  geese,  and  swans  (Lamellirostres). — The  birds 
of  this  order,  with  their  broad,  flat,  serrated  beaks,  short 
legs,  and  webbed  feet,  are  well  known,  for  in  a  wild  or 
domesticated  state  they  extend  all  over  the  earth.  All  are 
excellent  swimmers,  many  dive  remarkably  well,  and  are 
strong  on  the  wing.  While  a  considerable  number  breed 
within  the  United  States,  their  nesting-grounds  are  gener- 
ally farther  north,  and  in  the  early  spring  it  is  not  unusual 
to  see  them  migrating  in  flocks  from  their  warmer  winter 
homes.  Among  the  ducks,  the  mergansers,  mallards  (from 
which  our  domestic  species  have  been  derived),  the  teals, 
and  the  beautiful  wood-duck  remain  with  us  the  year 
round,  dwelling  on  quiet  streams  and  shallow  ponds,  living 
on  fish,  Crustacea,  and  seeds.  In  the  more  open  waters  of  the 
larger  lakes  and  along  the  seacoast  we  find  the  canvasback, 
the  scaup-ducks,  and  the  eiders  (Fig.  123)  which  supply  the 
famous  down  of  commerce.  Of  the  few  species  of  geese 
which  inhabit  the  United  States,  the  Canada  goose  (Brant a 
canadensis)  is  perhaps  the  most  familiar.  During  their 
migrations  to  the  nesting  sites  they  fly  in  V-shaped  flocks, 
their  "  honks  "  announcing  the  opening  of  spring.  The 
brant  (B.  bernicla)  is  also  common  in  the  eastern  part  of 
the  country,  where  it,  like  its  relations,  lives  on  vegetable 
substances  entirely.  The  swans  are  familiar  in  their  semi- 


FIG.  133. — American  eider-duck  (Somateria  dnxsti-i}. 


THE  BIRDS  215 

domesticated  state,  but  the  two  beautiful  wild  swans  found 
in  this  country  are  rarely  seen. 

201.  The  herons  and  bitterns  (Herodines). — The  herons 
and  bitterns  are  also  aquatic  in  their  habits,  but,  unlike  the 
swimming-birds,  they  seek  their  food  by  wading.    Adapting 
them  for  such  an  existence,  the  legs  and  neck  are  usually 
very  long,  and  the  bill,  longer  than  the  head,  is  sharp  and 
slender.     Among  the  relatively  few  species  in  the  United 
States,  the  great  blue  heron  (Ardea  herodias)  is  widely  dis- 
tributed, and  may  often  be  seen  standing  motionless  in 
some  shallow  stream  on  the  lookout  for   fish,  or  it  may 
wander  away  into  the  meadows  and  uplands  to  vary  its  diet 
with  frogs  and  small  mammals.     Even  more  familiar  is  the 
little  green  heron  or  poke  (Ardea  virescens),  which  also  is 
seen  widely  over  the  country.     The  night-herons,  as  their 
name  indicates,  stalk  their  prey  by  night,  and  during  the 
day  roost  in  companies — a  characteristic  common  to  most 
herons.     The  bitterns  or  stake-drivers  are  at  home  in  reedy 
swamps,  where  they  live  singly  or  in  pairs,  and  throughout 
the  night,  during  times  of  migration,  utter  a  booming  noise 
resembling  the  driving  of  a  stake  into  boggy  ground.     As 
a  rule,  the  herons  breed  as  they  roost — in  companies — build- 
ing bulky  platforms,  usually  in  trees.     The  bitterns,  on  the 
other  hand,  secrete  their  nests  on  the  ground  in  the  rushes 
of  their  marshy  home. 

202.  Cranes,  rails,  and  coots  (Paludicolae). — In  their  ex- 
ternal form  the  cranes  and  rails  resemble  the  herons,  but 
in  their   internal    organization   they   differ    considerably. 
They   likewise    inhabit  marshy  lands,  but  usually  avoid 
wading,  picking  up  the  frogs,  fish,  and  insects  or  plants 
along  the  shore  or  from  the  surface  of  the  water.    The  cranes 
are  comparatively  rare  in  this  country,  yet  one  may  occasion- 
ally meet  with  the  whooping-cranes  (Grus  americana)  and 
sand-hill  cranes  (Grus  mexicand),  especially  in  the  South 
and  West.     They  are  said  to  mate  for  life,  and  annually 
repair  to  the  same  breeding-grounds,  where  they  build  their 

15 


216  ANIMAL  FORMS 

nests  of  grass  and  weeds  on  the  ground  in  marshy  places. 
The  rails  are  more  abundant,  though  rarely  seen  on  ac- 
count of  their  habit  of  skulking  through  the  swamp 
grasses.  Only  rarely  do  they  take  to  the  wing,  and  then 
fly  but  a  short  distance,  with  their  legs  dangling  awk- 
wardly. Closely  related  to  them  are  the  coots  or  mud-hens 
(Fulica  americana),  which  may  be  distinguished,  however, 
by  their  slaty  color,  white  bills,  and  lobed  webs  on  the  toes, 
and  consequent  ability  to  swim.  All  over  the  United 
States  they  may  be  seen  resting  on  the  shores  of  lakes  or 
quiet  streams,  or  swimming  on  the  surface  gathering  food. 
The  nest  consists  of  a  mass  of  floating  reeds,  which  the 
young  abandon  almost  as  soon  as  hatched. 

203.  The  snipes,  sandpipers,  and  plovers  (Limicolse). — The 
snipes,  sandpipers,  and  plovers  are  usually  small  birds, 
widely  scattered  throughout  the  country  wherever  there 
are  sandy  shores  and  marshes.  In  most  species  the  legs 
are  long,  and  in  connection  with  the  slender,  sensitive  bill 
fit  the  bird  for  picking  up  small  animals  in  shallow  water 
or  probing  for  them  deep  in  the  mud.  During  the  greater 
part  of  the  year  they  travel  in  flocks,  but  at  the  nesting- 
season  disperse  in  pairs  and  build  their  nests  in  shal- 
low depressions  in  the  earth.  The  eggs  are  usually 
streaked  and  spotted,  in  harmony  with  their  surroundings, 
as  are  the  young,  which  leave  the  nest  almost  as  soon  as 
hatched. 

Fully  fifty  species  of  these  shore-birds  live  within  the 
confines  of  the  United  States.  Among  these  the  woodcock 
(Philohela  minor}  and  snipe  (Gallinago  delicald)  are  abun- 
dant in  many  places  inland,  where  they  probe  the  moist  soil 
for  food,  and  in  turn  are  eagerly  sought  by  the  sportsman. 
Even  more  familiar  are  the  sandpipers  and  plovers,  which 
are  especially  common  along  the  seacoast,  and  are  also 
abundantly  represented  by  several  species  far  inshore. 
Among  the  latter  are  the  well-known  spotted  sandpiper  or 
"tip-up"  (Actitis  macularid)  and  the  killdeer  plover 


THE   BIRDS 


21V 


alitis   vocifera),   which   inhabit  the   shores   of  lakes  and 
streams  throughout  the  country. 

204.  Quail,  pheasants,  grouse,  and  turkeys  ( Gallinae). — The 
quail,  grouse,  and  our  domestic  fowls  are  all  essentially 


FIG.  124.  —  California  quail  (Lophortyr  californicus).    Two-thirds  natural 


ground-birds,  and  their  structure  well  adapts  them  to  such 
a  life.  The  body  is  thick-set,  the  head  small,  and  the  beak 
heavy  for  picking  ope'n  and  crushing  the  seeds  and  berries 


218  ANIMAL  FORMS 

upon  which  they  live.  The  legs  and  feet  are  stout,  and 
fitted  for  scratching  or  for  running  through  grass  and 
underbrush.  Protective  colors  also  prevent  detection,  but 
if  close  pressed  they  rise  into  the  air  with  a  rapid  whirring 
of  their  stubby  wings,  and  after  a  short  flight  settle  to  the 
ground  again.  During  the  breeding-season  the  male  usu- 
ally mates  with  a  number  of  hens,  which  build  rough  nests 
in  hollows  in  the  ground,  where  they  lay  several  eggs.  The 
young  are  precocial. 

The  quail  or  bob-white  (Colinus  virginianus)  and  the 
ruffed  grouse  (Bonasa  umbellns)  occur  throughout  the 
Eastern  States.  Over  the  same  area  the  wild  turkey 
(Meleagris  gallopavo)  once  extended,  but  is  now  almost 
extinct.  The  prairies  of  the  middle  West  support  the 
prairie-hen  (Tympanuchus  americanus),  and  the  valleys 
and  mountains  of  the  far  West  are  the  home  of  several 
species  of  quails,  some  of  which  are  beautifully  crested. 

205.  Pigeons  and  doves  (Columbae). — The  pigeons  and 
doves  belong  to  a  small  yet  well-defined  order,  with  upward 
of  a  dozen  representatives  in  the  United  States.  They  are 
of  medium  size,  with  small  head,  short  neck  and  legs,  and 
among  other  distinguishing  characters  frequently  possess  a 
swollen,  fleshy  pad  in  which  the  nostrils  are  placed.  In 
former  years  the  passenger-pigeon  (Ectopistes  migrator i us), 
inhabiting  eastern  Xorth  America,  was  probably  the  most 
common  species  in  this  country.  Their  flocks  contained 
thousands,  at  times  millions,  of  individuals,  which  often 
traveled  hundreds  of  miles  a  day  in  search  of  food,  to  return 
at  night  to  definite  roosts — a  trait  which  enabled  the  hunter 
to  practically  exterminate  them.  At  present  the  mourning- 
or  turtle-dove  (Zenaidura  macroura)  is  the  most  familiar 
and  wide-spread  of  the  wild  forms.  The  domestic  pigeons 
are  all  descendants  of  the  common  rock-dove  (ColumM 
Uvid)  of  Europe,  the  numerous  varieties  such  as  the  tum- 
blers, fantails,  pouters,  etc.,  being  the  product  of  man's 
careful  selection.  In  the  construction  of  the  nest,  usually 


THE  BIRDS  219 

a  rude  platform  of  twigs,  and  in  the  care  of  the  young 
both  parents  have  a  share.  The  young  at  hatching  are 
blind,  naked,  and  perfectly  helpless,  and  are  fed  masticated 
food  from  the  crops  of  the  parents  until  able  to  subsist  on 
fruits  and  seeds. 

206.  Eagles,  hawks,  owls,  etc.  (Raptores). — The  birds  of 
prey,  all  of  which  belong  to  this  order,  are  carnivorous, 
often  of  large  size  and  great  strength,  and  are  widely  dis- 
tributed throughout  this  country.  The  vultures  live  on 
carrion,  some  of  the  small  hawks  and  owls  on  insects,  while 
the  majority  capture  small  birds  and  mammals  by  the  aid  of 
powerful  talons.  In  every  case  the  beak  is  hooked,  and  the 
perfection  of  the  organs  of  sight  and  hearing  is  unequaled 
by  any  other  animal,  man  included.  They  live  in  pairs, 
and  in  many  species  mate  for  life.  As  a  rule,  the  female 
incubates  the  eggs,  and  the  male  assists  in  collecting 
food. 

Among  the  vultures,  the  turkey-buzzard  (Cathartes  aura) 
is  most  abundant  throughout  the  United  States,  especially 
in  the  warmer  portions,  where  it  plays  an  important  part 
as  a  scavenger.  Of  the  several  species  of  hawks,  the  white- 
rumped  marsh-hawk  (Circus  hudsonius),  the  red-tailed 
hawk  (Buteo  borealis),  the  red-shouldered  hawk  (Buteo 
lineatus),  and  above  all  the  bold  though  diminutive  spar- 
row-hawk (Falco  sparverius)  are  the  most  abundant  and 
familiar.  In  the  more  unsettled  regions  live  the  golden 
eagle  (Aquila  chrysaetus)  and  bald  eagle  (Haliaetus  leuco- 
ceplialus).  The  owls  are  nocturnal,  and  not  so  often  seen 
as  the  other  birds  of  prey,  yet  the  handsome  and  fierce 
barn  or  monkey-faced  owl  (Strix pratincola},  and  the  larger 
species,  such  as  the  great  gray  owl  (Scotiaptex  cinereua), 
and  the  beautiful  snowy  owl  (Nyctea  nyctea],  are  more  or 
less  common,  and  occasionally  seen.  Much  more  abundant 
is  the  little  screech-owl  (Megascops  asio),  and  in  the  West- 
ern States  the  burrowing-owl  (Speotyto  cunicularia),  which 
lives  in  the  burrows  of  the  ground-squirrels  and  prairie- 


ANIMAL  FORMS 


dogs.     Fiercest  and  strongest  of  the   tribe  is  the  great 
horned  owl  (Bubo  virginianus). 


FIG.  125. -Bald  eagle  (Haliaetus  Ifucocephulugj. 

207.  Cuckoos  and  kingfishers  (Coccyges). — Omitting  the 
order  of  parrots  (Psittaci)',  whose  sole  representative  in  this 
country  is  the  almost  exterminated  Carolina  parrakeet 


THE  BIRDS  221 

(Conurus  carolinensis)^  we  next  arrive  at  the  cuckoos  and 
kingfishers,  which  differ  widely  in  their  habits.  The  black- 
or  yellow-billed  cuckoos  or  rain-crows  are  shy,  retiring 
birds,  with  drab  plumage,  and  though  seldom  seen  are  often 
fairly  abundant,  and  are  of  much  service  in  destroying 
insects.  Unlike  their  shiftless  European  relatives,  which 
lay  their  eggs  in  the  nests  of  others  birds,  they  build  their 
own  airy  homes  in  some  bush  or  hedgerow,  and  raise  their 
brood  with  tender  care.  The  belted  kingfisher  (Ceryle 
alcyon)  is  also  of  a  retiring  disposition,  and  spends  much 
of  its  time  on  some  branch  overlooking  the  water,  occa- 
sionally varying  the  monotony  by  dashing  after  a  fish,  or 
flying  with  rattling  cry  to  another  locality.  Their  nests 
are  built  in  holes  in  banks,  and  six  or  eight  young  are 
annually  reared. 

208.  The  woodpeckers  (Pici).— The  woodpeckers  are 
widely  distributed  throughout  the  world,  and  are  preemi- 
nently fitted  for  an  arboreal  life.  The  beak  is  stout  for 
chiseling  open  the  burrows  of  wood-boring  insects,  which  are 
extracted  by  the  long  and  greatly  protrusible  tongue.  The 
feet,  with  two  toes  directed  forward  and  two  backward,  are 
adapted  for  clinging,  and  the  stiff  feathers  of  the  tail  serve 
to  support  the  bird  when  resting.  Almost  all  are  bright- 
colored,  with  red  spots  on  the  head,  at  least  in  the  males, 
which  may  further  attract  their  mates  by  beating  a  lively 
tattoo  with  their  beaks  on  some  dry  limb.  The  glossy 
white  eggs  are  laid  in  holes  in  trees,  and  both  parents  are 
said  to  share  the  duties  of  incubation  and  feeding  the 
young.  Among  the  more  abundant  and  well-known  species 
is  the  yellowhammer  or  flicker  (Colaptes  auratus),  which 
extends  throughout  the  United  States.  Somewhat  less 
widely  distributed  is  the  red-headed  woodpecker  (Melaner- 
pes  erythroceplialus),  and  the  small  black-and-white  downy 
woodpecker  (Dryobates  pulescens}.  This  is  often  called 
sapsucker,  but  incorrectly  so,  as,  like  all  but  one  of  our  other 
woodpeckers  it  feeds  on  insects.  The  yellow-bellied  wood- 


222 


ANIMAL   FORMS 


pecker  (Sphyrapicus  varius)  is  a  real  sapsucker,  living  on 
the  juices  of  trees.  A  close  relative  of  the  red-headed 
woodpecker,  the  California  woodpecker  (Melanerpes  formi- 
civorus),  is  renowned  for  its  habit  of  boring  holes  in  bark 
and  inserting  the  acorns  of  the  live  oak.  Subsequently  the 
bird  returns,  and  breaking  open  the  acorns,  devours  the 
grubs  which  have  infested  them,  and  apparently  eats  the 
acorns  also. 

209.  Swifts,  humming-birds,  etc.  (Macrochires).— The  birds 
of  this  order  are  rapid,  skilful  fliers,  and  their  wings  are 
very  long  and  pointed.  The  feet,  on  the  other  hand,  are 


FIG.  126.— Night-hawk  ( Chordeiles  mrgimamts)  on  nest.    Photograph  by  H.  K.  JOB. 

small,  relatively  feeble,  and  adapted  for  perching  or  cling- 
ing. Accordingly,  the  insects  upon  which  they  feed  are 
taken  during  flight  by  means  of  their  open  beaks.  The 
night-hawk  (Chordeiles  virginianus),  roosting  lengthwise  on 
a  branch  by  day,  at  nightfall  takes  to  the  wing,  and  high 
in  the  air  pursues  its  food  after  the  fashion  of  a  swallow. 
In  the  same  haunts  throughout  the  United  States  the  whip- 


THE  BIRDS  223 

poorwill  (Antrostomus  vociferus)  occurs,  sleeping  by  day, 
but  active  at  night.  Neither  of  these  birds  constructs  nests, 
but  lays  its  streaked  and  mottled  eggs  directly  on  the 
ground.  The  chimney- swifts  (Chcetura pelayica],  swallow- 
like  in  general  form  and  habits,  but  very  unlike  the  swallows 


FIG.  127.— Anna  hummers  (one  day  old),  showing  short  bill  and  small  size  of  body. 
Compare  with  last  joint  of  little  finger. 

in  structure,  frequent  hollow  trees  or  unused  chimneys,  to 
which  they  attach  their  shallow  nests.  The  nearly  related 
humming-birds  are  chiefly  natives  of  tropical  America,  only 
a  few  species  extending  into  the  United  States.  Of  these 
the  little,  brilliantly  colored,  and  pugnacious  ruby  throat 
(Trocliilus  colubris]  is  the  most  widely  distributed.  Its 
nest,  like  that  of  other  hummers,  is  composed  of  moss  and 
lichens  bound  together  with  cobweb  and  lined  with  down. 

210.  Perching  birds  (Passeres).— The  remaining  birds, 
over  six  thousand  in  all,  belong  to  one  order,  the  Passeres 
or  perchers.  They  are  characterized  by  great  activity, 
interesting  habits,  frequently  by  exquisite  powers  of  song, 
and  in  addition  to  several  other  structural  arrangements 
have  the  feet  adapted  for  perching.  Their  nesting  habits 


224 


ANIMAL   FORMS 


differ  widely,  but  in  every  case  the  young  are  helpless  at 
the  time  of  hatching,  and.  require  the  care  of  the  parents. 

The  perchers  constitute  the  greater  number  of  the  birds 
living  in  the  meadows  and  woods,  and  are  more  or  less 


Fia.  128. — Anna  hummer  (Calypte  anna)  on  nest. 

common,  and  consequently  familiar  everywhere.  Among 
the  families  into  which  the  order  is  divided  that  of  the  fly- 
catchers (TyrannidcB),  the  crows  and  jays  (CorvidcB),  the 
orioles  and  blackbirds  (Icteridce),  the  finches  and  sparrows 
(Fringillid<B)i  the  swallows  (Hinindinidce),  the  warblers 
(Mniotiltidce),  the  thrushes, robins,  and  bluebirds  (Turd idee), 
are  the  more  familiar,  though  the  others  are  equally  inter- 
esting. 


CHAPTEE   XVIII 

THE    MAMMALS 

211.  General  characteristics. — The  mammals,  constituting 
the  last  and  highest  class  of  the  vertebrates,  comprise  such 
forms  as  the  opossum  and  kangaroo,  the  whales  and  por- 
poises, hoofed  and  clawed  animals,  the  monkeys  and  man. 
All  are  warm-blooded,  air-breathing  animals,  having  the 
skin  more  or  less  hairy.  The  young  are  born  alive,  except 
in  the  very  lowest  forms,  which  lay  eggs  like  reptiles,  and 
for  some  time  after  birth  are  nourished  by  milk  supplied 
from  the  mammary  glands  (hence  the  word  mammals)  of 
the  mother.  The  skeleton  is  firm,  the  skull  and  brain 
within  are  relatively  large,  and,  with  few  exceptions,  four 
limbs  are  present. 

Most  of  the  mammals  inhabit  dry  land.  A  number, 
however,  such  as  the  whales  and  seals,  are  aquatic ;  while 
others,  such  as  the  beavers,  muskrats,  etc.,  though  not 
especially  adapted  for  an  aquatic  life,  are,  nevertheless, 
active  swimmers,  and  spend  much  of  their  time  in  the 
water. 

Mammals  tend  to  associate  in  companies,  as  we  may 
witness  among  the  ground-squirrels,  prairie-dogs,  rats, 
mice,  and  the  seals  and  whales.  In  many  cases  they  band 
for  mutual  protection,  and  often  fight  desperately  for  one 
another.  Claws,  hoofs,  and  nails  are  efficient  weapons,  and 
spiny  hairs,  as  on  the  porcupines,  bony  plates,  such  as 
encircle  the  bodies  of  the  armadillos,  and  thick  skin  and 
hair,  serve  as  a  protection.  The  hair  is  also  frequently 
colored  to  harmonize  the  animal  with  its  surroundings. 

225 


226  ANIMAL   FORMS 

Some  rabbits  and  hares  in  the  far  north  don  a  white  coat 
in  the  winter  season. 

212.  Skeleton. — As    in  other  vertebrates,  the   external 
form  of  mammals  is  dependent  in  large  measure  upon  the 
internal    skeleton.      This   consists   of    relatively   compact 
bones,  the  cavities  of  which  are  filled  with  marrow.     Those 
forming  the  skull  are  firmly  united,  and,  as  in  other  verte- 
brates, afford  lodgment  for  several  organs  of  special  sense 
and  for  the  brain,  which,  like  that  of  the  birds,  completely 
fills  the  cavity  in  which  it  rests.     The  vertebral  column  to 
which  the  skull  is  attached  differs  considerably  in  length, 
but  it  invariably  gives  attachment  to  the  ribs,  and  to  the 
basal  girdles  supporting  one  or  two  pairs  of  limbs.     Gener- 
ally speaking,  the  number  of  bones  in  the  head  and  trunk 
of  all  mammals  is  the  same,  so  the  variations  we  note  in 
the  species  about  us,  for  example,  are  simply  due  to  differ- 
ences of  shape  and  proportion.     As  we  are  aware,  there  is  a 
great  dissimilarity  between  the  length  of  the  neck  of  man 
and  that  of  the  giraffe,  yet  the  number  of  bones  in  each 
is  precisely  the  same.     On  the  other  hand,  the  variations 
occurring  in  the  limbs  are  often  due  to  the  actual  disap- 
pearance of  parts  of  the  skeleton.     Five  digits  in  hand 
and  foot  is  the  rule,  and  yet,  as  we  well  know,  the  horse 
walks  on  the  tip  of  its  middle  finger  and  toe,  the  others 
being  represented  by  small,  very  rudimentary,  splint  bones 
attached  far  up  the  leg.     The  even-hoofed  animals  walk  on 
two  digits,  two   smaller  hoofed  toes   being  often   plainly 
visible  a  short  distance  up  the  leg,  as  in  the  pig.     In  the 
whales  the  hind  limbs  have  completely  disappeared,  and  in 
the   seals,  where  the  fore  limbs   are  modified,  as   in  the 
whales,  into  flippers,  the  hind  limbs  show  many  signs  of 
degeneration. 

213.  Digestive  system. — Some   mammals,  such  as  man, 
monkeys,  and  pigs,  are  omnivorous ;  others,  like  the  cud- 
chewers  and  gnawers,  are  vegetarians ;    and  still   others, 
like  the  foxes,  weasels,  and  bears,  are   carnivorous.      In 


THE  MAMMALS  227 

every  case  the  food  substances  are  acted  on  by  a  digestive 
system  constructed  on  the  same  general  plan  as  that  in  man, 
yet  modified  according  to  the  specific  work  it  is  required  to 
perform.  The  teeth  especially  afford  a  valuable  indication 
of  the  animal's  feeding  habits,  and,  as  we  may  notice  later, 
are  also  of  much  value  in  classification.  They  consist  of 
incisors  used  in  biting,  canines  for  tearing,  and  premolars 
and  molars  for  crushing  and  grinding. 

The  remaining  portions  of  the  digestive  tract,  esopha- 
gus, stomach,  and  intestine,  with  their  appended  glands,  are 
usually  not  unlike  these  possessed  by  the  squirrel  (Fig.  1). 
The  chief  differences  are  in  the  size  of  the  various  regions. 
The  stomach,  for  example,  may  be  long  and  slender  or  of 
great  dimensions,  and  its  surface  may  further  be  increased 
by  several  lobes,  which  are  especially  well  developed  in  the 
ruminants  or  cud-chewers.  The  intestine,  relatively  longer 
in  the  mammals  than  in  any  other  class  of  vertebrates,  also 
exhibits  great  differences  in  length  and  size.  In  the  flesh- 
eating  species  its  length  is  about  three  or  four  times  the 
length  of  the  body,  while  in  the  ruminants  it  is  ten  or 
twelve  times  the  length  of  the  animal. 

214.  Nervous  system  and  sense-organs. — As  before  noted, 
the  nervous  system  of  mammals  is  characterized  by  the 
large  size  and  great  complexity  of  the  brain.  Even  in  the 
simpler  species  the  cerebral  hemispheres  (large  front  lobes 
of  the  brain,  Fig.  1)  are  well  developed,  and  in  the  higher 
forms  of  the  ascending  series  they  form  by  far  the  larger 
part  of  the  brain.  The  sense-organs  also  are  highly  de- 
veloped, and  are  constructed  and  located  much  as  they  are 
in  man.  The  greatest  variations  occur  in  the  eyes.  In 
some  of  the  burrowing  animals  they  are  usually  small,  and 
in  some  of  the  moles  and  mice  may  even  be  buried  beneath 
the  skin  and  very  rudimentary.  On  the  other  hand,  they 
are  large  and  highly  organized  in  nocturnal  animals ;  more 
so,  usually,  than  in  those  which  hunt  their  prey  by  day. 
The  ears  also  have  different  grades  of  perfection,  which 


228  AXIMAL  FORMS 

appear  to  be  correlated  with  the  habits  of  the  animal. 
Among  the  species  of  subterranean  habits  the  sense  of  hear- 
ing is  largely  deficient ;  but,  on  the  other  hand,  it  is  ex- 
ceedingly keen  in  the  ruminants,  and  enables  them  to  detect 
their  enemies  at  surprisingly  great  distances.  In  these 
creatures  the  outer  ears  are  of  large  size  and  great  mobility, 
and,  placed  as  they  are  on  the  top  of  the  head,  serve  to  con- 
centrate the  sound-waves  on  the  delicate  apparatus  within. 
In  the  mammals  the  sense  of  smell  reaches  its  highest  de- 
velopment, especially  among  the  carnivores  which  scent  their 
prey.  On  the  other  hand,  it  is  said  to  be  absent  in  the 
whales  and  very  deficient  in  the  seals.  The  sense  of  taste, 
closely  related  to  that  of  smell,  is  located  in  taste-buds  on 
the  tongue,  and  is  also  more  acute  than  in  any  other  class  of 
animals.  The  sense  of  touch,  located  over  the  surface  of 
the  body,  is  especially  delicate  on  the  tips  of  the  fingers, 
the  tongue,  and  lips,  which  often  bear  long  tactile  hairs, 
called  whiskers  or  vibrissee. 

215.  Mental  qualities. — Correlated  with  the  high  degree 
of  perfection  of  the  brain  and  sense-organs  the  mammals 
show  a  higher  degree  of  development  of  the  intellectual 
faculties  than  any  other  class  of  animals.     In  many  cases 
their  acts  are  instinctive,  and  not  the  result  of  previous 
training  and  experience.     Just  as  the  duck  hatched  in  an 
incubator  instinctively  takes  to  the  water  and  pecks  at  its 
food,  or  as  the  bee  builds  its  symmetrical  comb,  many  of 
the  mammals  perform  their  duties  day  by  day.     On  the 
other  hand  many  other  mammals  are  also  undoubtedly  in- 
telligent.    They  possess  the  faculty  of  memory ;  they  form 
ideas  and  draw  conclusions  ;  they  exhibit  anger,  hatred,  and 
self-sacrificing  devotion  for  their  companions  and  offspring 
that  is  different  from  that  in  man  only  in  degree  and  not 
in  kind.     In  fact,  intelligence  differs  from  instinct  primar- 
ily in  its  power  of  choice  among  lines  of  action. 

216.  Classification. — Of  the  eleven  orders  into  which  the 
mammals  have  been  divided  eight  are  represented  in  this 


FIG.  129.— Three-toed  sloth  (Bradypus).    About  one-tenth  natural  size. 


230  ANIMAL  FORMS 

country.     Of  the  other  three  the  first  (Monotremes)   and 
simplest   of   the  eleven   is   represented   by  the  duck-mole 


> 


FIG.  180.— Australian  duck-mole  (Ornithorhynchus  paradoxus).    One-fifth  natural 


6ize. 


(Ornithorliynclms)    living  in  the  Australian    rivers.     Its 
general  appearance  and  mode  of  life  are  represented  in 


THE  MAMMALS 


231 


Fig.  130.  The  duck-moles  are  the  only  mammals  which 
lay  eggs.  One  egg  a  year  is  deposited  in  a  carefully  con- 
structed nest  where  the  young  are  hatched.  Another  order 
(Edentata)  includes  a  number  of  South  and  Central  Ameri- 
can forms,  among  which  are  the  ant-eaters,  armadillos, 
and  tree-inhabiting  sloths  (Fig.  129).  Still  another  order 
(Sirenia)  includes  the  fish-shaped  marine  dugong  and  sea- 
cows  or  manatees,  of  which  one  species  is  found  occasion- 
ally on  the  Florida  coast.  The  remaining  orders  are  de- 
scribed in  the  succeeding  sections. 

217.    The    opossums  and  kangaroos  (Marsupialia).— The 
lowest  order  of  mammals  represented  in  the  United  States 


FIG.  131. — Opossum  (Didelphys  virginiana).     One-tenth  natural  size.    Photograph 
by  W.  H.  FISHER. 

is  that  of  the  marsupials.     It  includes  the  opossums  and 
kangaroos,  together  with  a  number  of  comparatively  small 
and  unfamiliar  animals  living  chiefly  in  and  about  Australia. 
16 


232  ANIMAL  FORMS 

The  opossums,  fairly  abundant  throughout  the  warmer 
portions  of  this  country,  are  rat-like  creatures,  with  scaly 
tails,  yellowish-white  fur,  large  head,  and  pointed  snout. 
Except  at  the  breeding  season  they  lead  solitary  lives, 
sleeping  in  the  holes  of  trees  by  day  and  at  night  feeding 
on  roots,  birds,  and  fruits. 

The  kangaroos,  familiar  from  specimens  in  menageries 
or  museums,  chiefly  inhabit  the  plains  of  Australia.  The 
giant  gray  kangaroos  (Macropus  giyanteus],  attaining  a 
height  of  over  six  feet,  go  in  herds,  and  owing  to  the  great 
development  of  their  hind  limbs  and  tails  are  able,  when 
alarmed,  to  travel  with  the  swiftness  of  a  horse.  Several 
smaller  species,  some  no  larger  than  rabbits,  live  among 
the  brush,  and  like  their  larger  relatives  crop  the  grass  and 
tender  herbage  with  sharp  incisor  teeth. 

While  the  marsupials  do  not  lay  eggs  as  does  the  duck- 
mole,  they  allow  them  to  develop  within  the  body  for  a 
very  short  time  only.  Hence  the  young,  when  born,  are 
scarcely  more  than  an  inch  in  length,  and  are  blind,  naked, 
and  perfectly  helpless.  At  once  they  are  placed  by  the 
mother  in  the  pouch  of  skin,  or  marsupium,  on  the  under 
side  of  her  body.  In  this  the  young  are  suckled  and  pro- 
tected until  able  to  gather  their  own  food  and  fight  their 
own  way. 

218.  Rodents  or  gnawers  (Glires).— The  rodents  are  a 
large  group  of  mammals,  including  such  forms  as  the  rats, 
mice,  squirrels,  gophers,  and  rabbits.  They  are  readily  dis- 
tinguished by  their  clawed  feet  adapted  for  climbing  or 
burrowing,  and  by  large  curved  incisor  teeth.  Unlike 
ordinary  teeth,  they  grow  continually,  and,  owing  to  the 
restriction  of  the  hard  enamel  to  their  front  surfaces,  wear 
away  behind  faster  than  in  front,  thus  producing  a  chisel- 
like  cutting  edge. 

The  largest  of  our  native  rodents  is  the  porcupine 
(Eretliizon  dorsatus),  which  ranges  from  Maine  to  Mexico, 
and  attains  a  length  of  nearly  three  feet.  Many  of  the  hairs 


THE   MAMMALS 


233 


of  the  body  have  the  form  of  stiff,  barbed  spines  (Fig.  132), 
readily  dislodged  so  that  the  animal  requires  no  other  wea. 
pon  of  defense.  The  rabbits  and  hares  are  of  smaller  size, 
and  the  cottontails  especially  are  widely  distributed.  West 
of  the  Mississippi  the  jack-rabbits  are  familiar,  and  are 


•  FIG.  132. — Porcupine  (Hystrix  cristata).    One-tenth  natural  size. — After  BREHM. 

famous  for  their  great  speed.  Like  the  porcupines,  they 
feed  on  leaves  and  grass,  and  are  often  very  destructive. 
The  mice,  especially  the  field  and  white-footed  mice,  are 
abundant  in  woodland  and  meadow  throughout  the  United 
States.  The  house-mouse  (Mus  musculus)  is  a  native  of 
Europe,  as  is  the  common  rat  (M.  decumanus),  which  was 
imported  over  a  century  ago.  The  wood-rat  (Neotoma), 
however,  is  native,  and  may  be  found  in  many  localities 
from  east  to  west.  The  muskrat  (Fiber  zibethicus),  beaver 
(Castor  canadensis),  and  woodchuck  (Arctomys  monax)  were 
also  more  or  less  plentiful  formerly,  but  in'irtany  localities 
are  well-nigh  exterminated.  The  squirrels,  on  the  other 
hand,  continue  to  exist  in  large  numbers.  The  prairie- 


234  ANIMAL  FORMS 

dogs,  ground-squirrels,  and  chipmunks  of  the  terrestrial 
species  are  of  frequent  occurrence,  and  of  the  tree-dwellers 
the  fox,  gray  and  red  squirrels  are  well  known  in  many 
sections  of  the  United  States. 

219.  Insect-eating  mammals   (Insectivora). — The  shrews 
and  moles  belonging  to  this  order  are  representatives  of  a 
large   group   of   small  animals,  which,  unlike  the  major 
number  of  rodents,  live  on  insects.     The  shrews,  of  which 
there  are  several  species  in  this  country,  are  small,  mouse- 
like creatures,  nocturnal  in  their  habits,  and  hence  rarely 
seen.     The  moles  are  of  much  larger  size,  and  owing  to 
their  burrowing   proclivities   scarcely   ever  appear  above 
ground,  but  excavate  elaborate  burrows  with  their  shovel- 
like  feet,  devouring  the  insects  which  fall  in  their  way.    The 
common  mole  (Scalops  aquaticus)  extends  from  the  eastern 
seaboard  to  the  Mississippi  River,  where  it  is  replaced  by 
the  prairie-mole  (S.  argenteus),  which  extends  far  to  the 
west,  into  a  country  inhabited  by  other  species. 

220.  The  bats  (Cheiroptera).— The  bats  are  also  insectiv- 
.  orous,  but  their  habits  are  widely  different  from  those  of 

the  shrews  and  moles.  The  forearm  and  the  fingers  of  the 
fore  limbs  are  greatly  elongated,  and  are  connected  by  a 
thin  papery  membrane,  which  also  includes  the  hind  limbs 
and  tail,  and  serves  as  an  efficient  organ  of  flight.  During 
the  day  they  remain  suspended  head  downward  in  some 
dark  cranny,  awakening  at  nightfall  to  capture  flying 
insects.  Several  species  are  found  in  this  country,  the 
most  common  being  the  little  brown  bat  ( Vespertilio  fus-, 
cus),  with  small,  fox-like  face,  large  erect  ears,  and  short 
olive-brown  hair.  The  red  bat  (Lasiurus  borealis)  is  also 
plentiful  everywhere  throughout  the  United  States,  and  is 
distinguished  from  the  preceding  by  its  somewhat  larger 
size  and  long  reddish-brown  fur. 

221.  The  whales    and   porpoises    (Cete).— The    animals 
belonging  to  this  order,  the  whales  (Fig.  133),  porpoises,  and 
dolphins,  are  aquatic  animals  bearing  a  resemblance  to  fishes 


THE   MAMMALS 


235 


only  in  external  form.    The  cylindrical  body  has  no  distinct 
neck,  the  comparatively  large  head  uniting  directly  with 


the  cylindrical  body,  which  terminates  in  the  tail  with  hori- 
zontally placed  fins.     Xo  external  signs  of  hind  limbs  exist, 


236  ANIMAL  FORMS 

while  the  fore  limbs  are  short  and  capable  of  being  moved 
only  as  a  whole.  External  ears  are  also  absent.  The  eyes 
are  exceedingly  small,  those  of  individuals  attaining  a  length 
of  from  fifty  to  eighty  feet,  being  in  some  species,  at  least, 
but  little  larger  than  those  of  an  ox.  These  are  often  placed 
at  the  corners  of  the  mouth.  The  nasal  openings,  often 
known  as  blow-holes,  are  situated  on  the  forehead,  and  as 
the  whale  comes  to  the  surface  for  air  afford  an  outlet  for 
the  stream  of  breath  and  vapor  often  blown  high  in  the 
air — a  process  known  as  spouting.  In  some  of  the  whales, 
such  as  the  dolphin,  porpqise,  and  sperm-whales,  the  teeth 
persist  throughout  life,  but  in  most  of  the  larger  species 
they  never  "  cut  "  the  gum,  but  early  disappear,  and  their 
place  is  taken  by  large  numbers  of  whalebone  plates  with 
frayed  edges  which  act  as  strainers.  The  smaller-toothed 
forms  (porpoises,  dolphins,  and  several  species  of  grampus) 
are  frequently  seen  close  to  the  shore,  where  they  are  usu- 
ally actively  engaged  in  capturing  fish.  On  the  other  hand, 
the  larger  species,  such  as  the  humpback,  right  whale,  and 
sulfurbottom,  not  uncommon  along  our  coasts,  especially 
to  the  northward,  live  on  much  smaller  organisms.  With 
open  mouth  these  whales  swim  through  the  water  until 
they  collect  a  sufficient  quantity  of  jelly-fishes,  snails,  and 
Crustacea,  then  closing  the  mouth  strain  out  the  water 
through  the  whalebone  fringes  and  swallow  the  residue. 

As  noted  above,  the  animals  of  this  order  are  almost 
wholly  devoid  of  hair,  but  the  heat  of  the  body  is  retained 
by  a  thick  layer  of  fat  beneath  the  skin.  This  "  blubber  " 
also  gives  lightness  to  the  body  (as  do  the  voluminous  lungs), 
and,  furthermore,  yields  large  quantities  of  oil,  which  in 
former  times  made  "  whale-fishing  "  a  profitable  industry. 
The  whales  bear  one,  rarely  two  offspring,  which  are  solicit- 
ously attended  by  the  mother  for  a  long  time.  The  smaller 
species  grow  to  a  length  of  from  five  or  eight  feet  (por- 
poises, dolphins)  to  twice  this  size  (grampuses) ;  while  the 
larger  whales,  by  far  the  largest  of  animals,  range  from 


THE  MAMMALS  237 

thirty  to  over  a  hundred  feet  in  length  with  a  weight  of 
many  tons. 

222.  Hoofed  mammals  (Ungulata). — The  order  of  hoofed 
animals  or  ungulates  includes  a  large  number  of  forms  like 
the  zebra,  elephant,  hippopotamus,  giraffe,  deer,  and  several 
other  wild  species,  some  of  which  are  domesticated,  such 
as  horses,  sheep,  goats,  and  cattle.  All  of  these  animals 
walk  on  the  tips  of  their  toes,  and  the  claws  have  become 
developed  into  hoofs.  The  order  is  divided  into  the  odd- 
toed  forms  (perissodactyls),  such  as  the  rhinoceros  with 
three  toes  and  the  horse  with  one,  and  the  even-toed  (artio- 
dactyls),  as  the  pigs  with  four,  and  the  ox,  deer,  etc.,  with 
two  toes.  The  even-toed  forms  are  again  divided  into 
those  which  chew  the  cud  (ruminants)  and  those  which  do 
not  (non-ruminants).  Xo  living  native  odd-toed  mammal 
exists  in  this  country,  and  of  the  wild  even-toed  species  all 
are  ruminants.  In  the  members  of  this  latter  group  the 
swallowed  food  passes  into  a  capacious  sac  (the  paunch),  is 
thoroughly  moistened,  and  passed  into  the  second  division 
(the  honeycomb),  later  to  be  regurgitated  and  ground  by 
the  powerful  molars.  It  is  then  reswallowed,  and  under- 
goes successive  treatment  in  the  other  two  divisions  of 
the  stomach  (the  manyplies  and  reed)  before  entering  the 
intestine. 

Among  the  Xorth  American  ruminants,  the  deer  fam- 
ily (Cervidce)  is  the  best  represented.  In  the  more  unsettled 
regions  of  the  East  the  red  deer  is  still  common,  and  the 
same  may  be  said  of  the  white-tailed,  black-tailed,  and 
mule-deer  of  the  West.  Among  the  woods  and  lakes  to 
the  northward  live  the  reindeer  and  caribou,  and  the  largest 
of  the  deer  family,  the  moose,  which  attains  the  size  of  the 
horse.  Of  nearly  the  same  size  is  the  wapiti  or  elk,  whose 
general  characters  are  shown  in  Fig.  134.  In  all  of  the 
above-mentioned  species  the  horns,  if  present,  are  confined 
to  the  male  (except  in  the  reindeer),  and  are  annually  shed 
after  the  breeding  season. 


THE   MAMMALS  239 

The  native  hollow-horned  ruminants  (Bovidce)  are  at 
present  confined  to  the  Western  plains,  and  comprise  the 
pronghorn  antelope  (Antilocapra  americana),  the  wary  big- 
horn or  Kocky  Mountain  sheep  (Ovis  canadensis),  living 
in  mountain  fastnesses,  and  the  buffalo  or  bison  (Bison 
bison).  All  of  these  species  were  formerly  abundant, 
especially  the  pronghorn  and  buffalo,  which  roamed  the 
plains  by  thousands,  but  their  extermination  has  been 
nearly  complete,  small  herds  only  persisting  in  a  few  wild, 
inaccessible  regions,  or  protected  in  parks. 

Our  domestic  sheep  and  cattle  are  probably  the  descend- 
ants of  several  wild  species  living  in  Europe  and  other 
portions  of  the  world.  Of  the  domesticated  even-toed 
ungulates  the  horse  is  the  direct  descendant  of  Asiatic 
wild  breeds  ;  while  the  pig  traces  its  ancestry  back  to  the 
wild  boar  (Sus  scrofa)  of  Europe,  and  probably  a  native 
species  (S.  indicus)  of  eastern  Asia. 

223.  Flesh-eating  mammals  (Ferae). — The  order  of  Ferae 
or  Carnivora  is  typically  exemplified  by  such  animals  as  the 
lions,  tigers,  bears,  dogs,  cats,  and  seals,  forms  which  differ 
from  all  other  mammals  by  the  large  size  of  the  canine  teeth 
(often  called  dog-teeth)  and  the  molars,  which  are  adapted 
for  cutting,  not  crushing.  The  limbs,  terminated  by  four 
or  five  flexible  digits,  bear  well-developed  claws,  which,  to- 
gether with  the  teeth,  serve  for  tearing  the  prey.  While 
the  bears  shuffle  along  on  the  soles  of  their  feet,  the  greater 
number  of  species,  as  illustrated  by  the  dog  and  cat,  tread 
noiselessly  on  tiptoe.  Almost  all  are  fierce  and  bold,  with 
remarkably  keen  senses  and  quick  intelligence,  and  are  the 
dreaded  enemies  of  all  other  orders  of  mammals. 

The  largest  land-inhabiting  carnivora  are  the  bears,  of 
which  the  brown  or  cinnamon  bear  ( Ursus  americanus], 
inhabiting  Xorth  America  generally  where  not  extermi. 
nated,  and  the  huge  grizzly  ( Ursus  horribilis)  of  the  West- 
ern mountains,  are  the  best-known  species.  The  former 
lives  on  berries  and  juicy  herbs,  while  the  grizzly  prefers 


240 


ANIMAL  FORMS 


the  flesh  of  animals  which  it  kills.  The  raccoon  (Fig.  135) 
(Procyon  lotor]  is  found  in  wooded  districts  all  over  the 
United  States,  and  its  general  appearance  and  thieving 
propensities  are  well  known.  Almost  everything  is  accept- 


able as  an  article  of  food,  and  its  fondness  for  poultry  and 
vegetables  makes  it  an  unmitigated  nuisance.  The  otters, 
skunks,  badgers,  wolverenes,  sables,  minks,  and  weasels,  while 
differing  considerably  in  general  appearance  and  habits,  nev- 


THE  MAMMALS 


241 


ertheless  belong  to  one  family  (the  weasel  family,  Mustelidce), 
and  are  more  or  less  valued  for  their  fur.  Almost  all  are 
characterized  by  a  .fetid  odor,  especially  the  skunk,  which 
is  notoriously  offensive,  and  in  consequence  is  avoided  by 
all  other  animals. 

The  dog  family  is  represented  by  several  widely  distrib- 
uted varieties  of  the  red  fox  ( Vulpes  pennsylvanicus]  and 
gray  fox  ( Urocyon  cinereo-argentatus),  and  by  the  coyotes 


FIG.    136.— Silver   fox   (Vulpes  pennsylvanicus,   var.    argentatus).      Photograph 
by  \V.  K.  FISHER. 

(Canis  latrans]  and  wolves  (Ganis  nubilus}.  The  domestic 
dog  (C'anis  familiar  is)  is  probably  the  descendant  of  the 
wolf,  and  owing  to  man's  careful  breeding  during  thou- 
sands of  years  has  formed  several  widely  differing  varieties. 
The  cat  family,  comprising  the  most  powerful,  savage, 
and  keenest-scented  carnivora,  is  represented  by  the  lion, 
tiger,  jaguar,  and  hyena.  In  this  country  the  group  is 
represented  by  the  lynx  (Lynx  canadensis),  the  wildcat 
(Lynx  ntfus),  and  the  panther  or  puma  (Felis  concolor), 
which  attains  the  length  of  nearly  five  feet.  The  domestic 
cat  has,  like  the  dog,  been  domesticated  for  centuries,  and 
has  possibly  descended  from  an  African  species  (Felis 


FIG.  137.— Panthers  (Felis  concdor)  and  peccaries  (Dicotylts  torquatw). 


THE   MAMMALS 


243 


caff r a),  which  was  held  sacred  by  the  Egyptians,  who  em- 
balmed them  by  thousands. 

224.  Man-like  mammals  (Primates).— The  last  and  high- 
est order  of  mammals,  the  Primates,  includes  the  lemurs, 
monkeys,  and  man.  The  first  of  these  are  strange  squir- 
rel-like forms  living  chiefly  in  trees  in  Madagascar  and 
neighboring  regions  where  they  feed  on  insects.  The  apes 
and  monkeys  are  divided  into  Old  and  Xew  World  forms, 
which  differ  widely  from  each  other.  The  American  species 
are  marked  by  flat  noses,  with  the  nostrils  far  apart.  All  are 
arboreal,  many  have  long  prehensile  tails,  and  the  digits  bear 
nails,  not  claws.  Among  them  are  several  species  of  marmo- 
sets, the  howling  monkeys  (Myocetes),  the  spider-monkeys 
(Ateles),  and  the  capuchins  (Cebus),  all  of  which  are  more  or 
less  common  in  captivity.  In  the  Old  World  apes,  on  the 
other  hand,  the  nostrils  are  close  together  and  are  directed 
downward,  the  tail  is  never 
prehensile,  and  in  some  cases 
is  rudimentary, and  may  even 
disappear.  The  lowest  spe- 
cies (the  dog-like  apes)  in- 
clude the  large,  clumsy  ba- 
boons, among  them  the  fa- 
miliar blue-nosed  mandrill 
(Cynocephalus  maimon)  and 
several  other  species  of  light- 
er frame,  such  as  the  long- 
tailed  monkey  (Cercopithe- 
cus)  (Fig.  139),  the  tailless 
Macacus,  common  in  menag- 
eries, and  the  Barbary  ape,  in- 
habiting northern  Africa  and 

extending  Over  into  Spain.          FIG-  1S8.— Baby  orang-utan.    From  life. 

The   remaining   anthro- 
poid or  man-like  apes  include  the  gibbons  (Hylobates),  orang- 
utan (Simia),  gorilla  (Gorilla],  and  chimpanzee  (Anthropo- 


FIG.  139. — A  monkey  (Cercopithecus)  in  a  characteristic  attitude  of  watchfulness. 


THE   MAMMALS 


245 


pithecus).  The  gibbons,  inhabiting  southeastern  Asia,  pos- 
sess arms  of  such  length  that  they  are  able  to  touch  their 
hands  to  the  ground  a's  they  stand  erect.  They  are  thus 
adapted  for  a  life  in  the  trees,  where  they  spend  most  of  their 
time  feeding  on  fruit,  leaves,  and  insects.  In  the  same  dis- 
trict the  orang  occurs,  walking  when  on  the  ground  on  its 
knuckles  and  the  sides  of  its  feet.  It  prefers  the  life  in 
the  trees,  however,  in 
which  it  builds  nests 
serving  for  rest  and 
concealment,  The  go- 
rilla (Fig.  140),  the 
largest  of  apes,  attain- 
ing a  height  of  over 
five  feet  and  a  weight 
of  two  hundred 
pounds,  is  a  native  of 
Africa,  where  it  lives 
in  families  and  sub- 
sists on  fruits.  The 
same  region  is  the 
home  of  the  chimpan- 
zee, which  in  its  vari- 
ous characteristics  ap- 
'proaches  most  nearly 
to  man. 

Man  (Homo  sapi- 
ens) is  distinguished 

by  the  inability  to  oppose  the  big  toe  as  he  does  his  thumb — 
a  feature  associated  with  his  erect  position — and  by  the  rela- 
tively enormous  size  of  the  brain.  Even  in  an  average  four- 
year-old  child  or  an  Australian  bushman  the  brain  is  twice  as 
large  as  in  the  gorilla.  With  this  relatively  great  develop- 
ment of  the  nervous  system  is  correlated  superior  mental 
faculties,  which  together  with  social  habits  and  powers  of 
speech  exalt  man  to  a  position  far  above  the  highest  ape. 


FIG.  140.-Gorilla  (Gorilla). 


246  ANIMAL  FORMS 

As  usually  understood,  the  family  of  man  (Hominidce) 
contains  but  a  single  species,  cosmopolitan  and  highly  vari- 
able. This  species  is  "now  split  up  into  many  subspe- 
cies or  races,  the  native  man  of  this  continent,  or  '  Ameri- 
can Indian,'  being  var.  americanus.  Other  races  now 
naturalized  in  America  are :  the  Caucasian  race,  var.  euro- 
pceus ;  the  Mongolian  race,  var.  asiaticus ;  and  the  negro 
race,  afer.  The  first  of  these  is  an  immigrant' from  Europe, 
the  second  from  Asia,  and  the  third  was  brought  hither 
from  Africa  by  representatives  of  var.  europaus  to  be  used 
as  slaves." 


CLASSIFICATION  OF  AKIMALS 

The  following  table  of  classification  is  designed  to  show  the  systematic  position 
of  the  more  important  animals  mentioned  in  the  text. 

ANIMAL  KINGDOM 

ONE-CELLED  ANIMALS: 

BRANCH- L  PROTOZO'A  (protos,  first ;  zoon,  animal) 
Class  I.  Rhizop'oda  (rhiza,  root ;  pous,  foot). 

Amw'ba,  Difflii'gia. 

Class  II.  Infuso'ria  (organisms  found  in  infusions). 
Order  1.  Flagella'ta  (flagellum,  a  whip). 

Euglen'a,  Codosig'a,  Panddrl'na,  Vol'vSx. 
Order  2.   Cilia'ta  (cilium,  an  eyelash). 
Paramoz'cium,  Vorticel'la. 

MANY-CELLED  ANIMALS  (Metazoa) : 

BRANCH  II.   PORIF  ERA  (porus,  pore ;  fero,  to  carry.) 
Class  I.  Porifera  (or  sponges). 

BRANCH  III.    CQELENTERA  TA  (animals  with  combined  body  and 

stomach  cavity) 
Class  I.  Hydrozo'a  (hydra,  water-serpent ;  zoon,  animal). 

Hydra,  Gonionemus,  Hydractiriia,  Portuguese  man-of-war. 
Class  II.  Scyphozo  a  (scyphos,  cup;  zoon,  animal). 

RJuizijs'toma,  Haliclys' tus. 
Class  III.  Actinozo'a  (actis,  a  ray ;  zoon,  animal). 

BRANCH  IV.   PLATYHELMIN  THES  *  (platus,  flat ;  helminthos, 

a  worm) 

Class  I.  Plata' da  (platus,  flat;  eidos,  likeness). 
Plana'ria,  Leptopla'na. 

*  For  purposes  of  convenience,  the  flatworms  (Platyhelminthes), 
roundworms  (Xematelminthes),  and  segmented  worms  (Annelids)  are 
combined  in  one  branch  (The  Worms)  in  the  text. 

17  247 


248  ANIMAL  FORMS 

Class  II.  TrematS  da  (trematodes,  pierced  with  holes,  from  the 
erroneous  belief  that  the  suckers  are  holes  into  the  body). 

Liver  fluke,  Epidel'la. 
Class  III.   Cesto'da  (cestos,  a  girdle;  eidos,  likeness). 

Tapeworm. 

BRANCH  V.   NEMATELMINTHES   (nema,  thread;  helminUios.   a 

worm) 
Class  I.  Nemato  da. 

Vinegar  eel  (Anguillula),  Trtchl'na,  horsehair  snake  (Gordius). 

BRANCH  VI.   NEMERTIN  EA  (nemertes,  a  sea-nymph) 
BRANCH  VII.  ROTIF  ERA  (rota,  a  wheel ;  fero,  to  carry) 

BRANCH  VIII.    ANNE  L  IDA  (annelus,  a  ring) 
Class  I.   Chaetop  oda  (cltaiie.  bristle;  pous,  foot). 
Order  1.  Polychae  te  (polus.  many ;  chaite,  bristle). 

Ner'eis,  Polyno'e,  Ser'pula,  Sabella. 
Order  2.   Oligochae  te  (oligos,few;  cJi a ite,  bristle). 

Earthworm  (Lum'bricus). 
Class  II.  Hirudin  ea  (hirudo,  a  leech). 

Leeches. 

Class  III.  Gephyrea  (gephura,  a  bridge,  because  these  animals  were 
once  supposed  to  bridge  the  gap  between  the  worms  and  sea- 
cucumbers). 

BRANCH  IX.   MOLLUSCOIDA 
Class  I.  PSlyzo'a  (polus,  many ;  zoon,  animal— colonial  animals). 

Polyzoa,  sea-mats. 
Class  II.  BrachiSp  oda  (brachion,  arm ;  pous,  foot). 

Lamp-shells  (brachiopods). 

BRANCH  X.   MOLLUS  CA  (mollin,  soft) 
Class  I.  Lamellibranchia  ta  (lamella,  a  plate;  bronchia,  gill). 

Clams,  mussels,  oysters,  ship-worm  (Tere'do). 
Class  II.   GastrSp  oda  (gaster,  stomach ;  pous,  foot). 

Snails,  slugs,  armadillo  snails,  naked  snails,  nudibranchs. 
Class  III.  OephalSp'oda  (cephale,  head ;  pous,  foot). 

Squids,  cuttlefishes,  devil-fishes  (Oc'topus),  nautilus. 

BRANCH   XI.   EOHINODER  MAT  A  (echinos,  a  hedgehog;  derma, 

skin) 

Class  I.   Asteroidea  (aster,  star;  eidos,  likeness). 
'Starfishes. 


CLASSIFICATION  OF  ANIMALS  249 

Class  II.   Ophiuroi'dea  (ophis,  serpent ;  oura,  tail ;  eidos,  likeness). 

Serpent-  or  brittle-stars,  basket-stars. 

Class    III.  Holothuroi  dea   (holotlmrion,  a  kind  of  water  polyp; 
eidos,  likeness). 

Sea-cucumbers. 
Class  IV.   Orinoi'dea  (crinon,  lily ;  eidos,  likeness). 

Sea-lilies  or  crinoids. 
Class  V.   Echinoi  dea  (echinos,  hedgehog;  eidos,  likeness). 

Sea-urchins. 

BRANCH  XII.   ARTHROF  ODA  (arthron,  joint ;  pous,  foot) 
Class  I.   Orusta  cea  (crusta,  a  crust  or  shell). 

Fairy-shrimp  (Brdnchip'us),  water-fleas  (Daph'nia),  cop'epod, 
Cy'clops,  goose  barnacle,  acorn  barnacle,  Saccull'na,  opossum- 
shrimp,  prawn,  lobster,  crayfish,  cancer-crab,  rock-crab,  pill- 
bug  or  i'sopod,  sand-hopper  or  amphi'pod. 
Class  II.   OnycSph'ora  (onyx,  claw ;  phero,  to  carry).  , 

Pertp'atus). 
Class  III.   Myribp  oda  (myrios,  numberless;  pous.  foot). 

Cent'iped,  thousand-legs. 

Class  IV.  Insec'ta  (insectum,  cut  in,  owing  to  the  grooves  surround- 
ing the  body). 

Fishmoth,  springtail,  cockroach,  grasshopper,  cricket,  katydid, 
locust,  dragon-fly,  caddis-fly,  may-fly,  white  ants  or  termites, 
ant-lion,  water-boatman,  water-bug,  back-swimmer,  chinch- 
bug,  squash-bug,  lice,  plant-lice,  Phijttox' era,  scale-insect, 
gnat,  mosquito,  flea,  house-fly,  stag-beetle,  wood-beetle,  water- 
beetle,  potato-beetle,  ladybug,  firefly,  moth,  butterfly,  ants, 
honey-bees  and  bumblebees,  wasps,  hornets,  yellow-jackets. 
Class  V.  Arach  nida  (arachne,  spider). 

Garden-spider,   taran'tula,   bird-spider,  trap-door  spider,  mite, 
tick,  king-crab  or  horseshoe  crab. 

BRANCH  XIII.  CHORDATA  (chorda,  a  cord,  referring  to  the 

notochord) 

SUBBRANCH  I.   Adelochor  da.     Class  Adelochorda. 
SUBBRANCH  II.   Urochor  da.     Class  Urochorda. 

Sea-squirts,  Tunica'ta,  Ascid'ians. 
SUBBRANCH  III.   Vertebra'ta  (vertebratus,  jointed). 

Division  A.   Acra'nia  (a,  without ;  cranion,  skull).    Class  Lepto- 

cardii. 

Lancelot  (Branchic'is'toma  =  Amphiox'us). 
Division  B.  Crania'ta. 


250  ANIMAL  FORMS 

Class  I.   Cyclostbm  ata  (cydos,  circle ;  stoma,  mouth). 
Hagfishes,  lamprey. 

Class  II.   Pis'ces  (piscis,  fish). 

Shark,  skate  or  ray,  lung-fish,  sturgeon,  garpike,  catfish,  horned 
pout,  bullhead,  carp,  dace,  chub,  minnow,  eel,  herring,  shad, 
salmon,  trout,  pike,  stickleback,  blindfish,  sea-horse,  mullet, 
flying-fish,  perch,  darter,  sunfish,  sea-bass,  mackerel,  snapper, 
grunt,  weakfish,  bluefish,  rose-fish,  gurnard,  sculpin,  codfish, 
flounder,  angler. 

Class  III.   Amphibia  (a  mphi,  double ;  bios,  life). 

Siren,  mud-puppy,  water-dog,  tiger  salamander,  axolotl,  toad, 
frog,  tree-frog. 

Class  IV.  ReptiTia  (reptans,  creeping). 

Skink,  "  glass-snake/'  swift,  chameleon,  horned  toad,  Gila  mon- 
ster, blacksnake,  grass-snake,  milk-snake,  rattlesnake,  copper- 
head, water-moccasin,  soft-shell  turtle,  snapper,  painted  turtle, 
box-turtle,  leather-turtle,  loggerhead,  hawkbill,  crocodile,  alli- 
gator. 

Class  V.   A'ves  (avis,  bird). 

Ostrich,  loon,  grebe,  auk,  murre,  puffin,  gull,  tern,  petrel,  alba- 
tross, cormorant,  pelican,  duck,  goose,  swan,  heron,  bittern, 
crane,  rail,  mud-hen  or  coot,  snipe,  woodcock,  sandpiper,  kill- 
dee  plover,  quail,  grouse,  wild  turkey,  prairie-chicken,  pigeon, 
dove,  eagle,  hawk,  owl,  turkey-buzzard,  cuckoo,  kingfisher, 
woodpecker,  sapsucker,  swift,  humming-bird,  night-hawk, 
whippoorwill,  crow,  jay,  swallow,  warbler,  thrush,  robin, 
bluebird. 

Class  VI.   Mammalia  (mamma,  breast). 

Duck-mole,  ant-eater,  sloth,  armadillo,  sea-cow,  opossum,  kanga- 
roo, porcupine,  mouse,  rat,  muskrat,  woodchuck,  beaver,  rabbit, 
squirrel,  chipmunk,  prairie-dog,  shrew,  mole,  bat,  whale,  gram- 
pus, dolphin,  porpoise,  zebra,  elephant,  giraffe,  deer,  antelope, 
goat,  sheep,  horse,  cow,  pig,  buffalo,  bear,  raccoon,  otter,  skunk, 
badger,  wolverene,  sable,  mink,  weasel,  dog,  fox,  wolf,  cat, 
lynx,  panther,  monkey,  ape,  baboon,  gibbon,  orang-utan, 
gorilla,  chimpanzee,  man. 


INDEX 


Acipenser  sturio  (illus.),  162. 

Acorn-barnacle  (illus.),  97. 

Air-bladder,  155. 

Albatross,  212. 

Alligator  mississippiensis  (illus.), 

191. 

Alternation  of  generations,  35. 
Altricial,  208. 
Amoeba  (illus.),  12;  structure  and 

habits,  12. 

Amoeba-like  protozoa,  12. 
Amphibian,  development  of,  174 ; 

distribution,  178 ;  anatomy  and 

habits,  179. 
Amphibious  (amphi,  double;  bios, 

life),  176. 

Amphioxus  (illus.),  157. 
Amphipod  (illus.),  106. 
Anatomy  (anatemno,  to  cut  up), 

defined,  1. 
Angler  (illus.),  169. 
Angle-worm  (illus.),  55. 
Anguillula  aceti  (illus.),  53. 
Animals,  characteristics  of,  2 ;  sim- 
ple and  complex,  18. 
Animals  and  plants  compared,  2. 
Annelids,  55. 

Anosia  plexippus  (illus.),  125. 
Ant,  128 ;  white  (illus.),  120. 
Anteater,  231. 
Antedon  (illus.),  148. 
Antelope,  239. 


Ant-lion  (illus.),  120. 

Apes,  243. 

Arachnida,  characteristics  of,  133. 

Arcliceopteryx,  201. 

Argynnis  cybele  (illus.),  126. 

Ariolimax  columbianus  (illus.),  81. 

Armadillo,  231. 

Arthropods,   general   features    of, 

93. 

Ascidian  (illus.),  152. 
Asexual  reproduction,  31. 
Aste'rias  ocracea  (illus.),  141. 
Astrophyton  (illus.),  143. 
Auk,  209. 
Axolotl,  183. 

Back-swimmer,  121. 
Balancers,  122. 
Band-worm  (illus.),  70. 
Barnacles  (illus.),  96. 
Bascanion  constrictor  (illus.),  187. 
Basket-star  (illus.),  141. 
Bass,  166. 

Bat,  brown,  234;  red,  234. 
Bear,  239. 
Beaver,  232. 
Bees,  238. 
Beetles,  124. 

Bell  animalcule  (illus.),  16. 
Bilateral  symmetry,  44. 
Biology  (bios,   life ;    logos,  a  dis- 
course) defined,  1. 

251 


252 


ANIMAL   FORMS 


Birds,  characteristics  of,  201 ;  anat- 
omy of,  204 ;  habits  of,  207. 

Bird  spider,  136. 

Bittern,  215. 

Black-snake  (illus.),  193. 

Blastula  (illus.),  21. 

Bombus  (illus.),  130. 

Bony  fish  (illus.),  160. 

Botany,  defined,  1. 

Brachiopod  (illus.),  70. 

Bradypus  tridactylus  (illus.),  229. 

Branchiostoma  californiense  (il- 
lustration), 157. 

Branchipus  (illus.),  94. 

Brittle-star  (illus.),  141 ;  regenera- 
tion of,  145. 

Bugs,  121. 

Bumblebee  (illus.),  130. 

Butterflies,  125. 

Buzzard,  219. 

Byssus,  77. 

Caddis-fly,  119. 

Calcolynthus  primigenius  (illus.), 

25. 

Calypte  anna  (illus.),  224. 
Cancer  productus  (illus.),  104. 
Caprella  (illus.),  106. 
Carapace,  of  Crustacea,  95,  99 ;  of 

turtle,  188. 
Carp,  163. 

Cat,  domestic,  239 ;  wild,  239. 
Catfish,  163. 
Cell  (cella,  a  little  room),  7 ;  shape 

and  size,  7;  typical  (illus.),  8. 
Centipeds  (illus.),  111. 
Cephalopod  (illus.),  87. 
Cephalothorax,  99. 
Cercopithecus  (illus.),  244. 
Cervus  canadensis  (illus.),  238. 
Cestode  (illus.),  50. 
Cete,  234. 


Cheiroptera,  234. 

Chelonia,  188. 

Chinch-bug,  122. 

Chiton  (illus.),  82. 

Chologaster  avetus  (illus.),  164 ;  C. 
agassizi  (illus.),  164. 

Chordate,  characteristics  of,  151. 

Chordeiles  virginianus  (illus.), 
222. 

Chub,  163. 

Cilium  (ciHum,  an  eyelash),  16. 

Circulatory  system,  use  of,  4. 

Clam  (illus.),  72 ;  anatomy,  72,  78  ; 
rock-  and  wood-boring,  75. 

Clitellum,  58. 

Coccyges,  220. 

Cockroach,  118. 

Ccelenterates,  general  character- 
istics of,  18. 

Coleoptera  (illus.),  124. 

Columbae,  210. . 

Complex  animals,  characteristics 
of,  18. 

Compound  eyes,  109. 

Coot,  215. 

Copperhead,  193. 

Corals  (illus.),  41. 

Cormorant,  212. 

Correlation  of  function  and  struc- 
ture, 6. 

Cottontail,  233. 

Courting  colors,  203. 

Crab,  hermit  (illus.),  102 ;  cancer 
(illus.),  103;  rock  (illus.),  104; 
fiddler,  104. 

Crane  (illus.),  215. 

Crayfish  (illus.),  101. 

Cricket,  118. 

Crinoid  (illus.).  143. 

Crocodile,  190. 

Crocodilia  (illus.),  190. 

Crolalus  adamanteus  (illus.),  222. 


INDEX 


253 


Crustacea,  93  ;  anatomy  of,  98,  107 ; 

multiplication  of,  98,  110. 
Cteniza  (illus.),  137. 
Cuckoo,  220. 
Cucumaria  (illus.),  146. 
Cuticle,  14. 
Cuttlefish,  87. 
Cutworm,  112. 
Cyclops  (illus.),   95 ;  anatomy  of. 

'98. 
Cyclostomes,  157. 

Daddy-long-legs,  130. 

Decapods,  102. 

Deer,  222. 

Dendrostoma  (illus.),  68. 

Devil-fish  (illus.),  87. 

Diddphys  virginiana  (illus.),  231. 

Diemyctylus  torosus  (illus.),  182. 

Digestive  tract,  use  of,  3. 

Diptera  (illus.),  119. 

Division  of  labor,  21. 

Dog,  223. 

Dolphin,  221. 

Dove,  205. 

Dragon-fly  (illus.),  118. 

Duck-mole  (illus.),  216. 

Ducks  (illus.),  200. 

Eagle,  golden,  205;  bald  (illus.), 
205. 

Earthworm  (illus.),  55:  anatomy, 
55 ;  distribution,  59. 

Echinoderms,  141 ;  locomotor  sys- 
tem, 146 ;  development  of,  150. 

Ecology,  1. 

Eel,  163. 

Egg,  fertilization  of,  20,  21. 

Elk  (illus.),  222. 

Encystment  of  protozoa,  13. 

Epialtus  produdus  (illus.),  104. 

Epidella  squamula  (illus.),  49. 


Eretmochelys     imbricata    (illus.), 

195. 

Esox  (illus.),  165. 
Euglena  (illus.),  17. 
Eurypelma  lentzii  (illus.),  136. 

Fairy  shrimp  (illus.),  94. 

Felis  concolor  (illus.),  242. 

Ferse,  239. 

Firefly,  124. 

Fish,  general  characters  of,  154; 

respiration,  155 ;  anatomy,  168 ; 

breeding  habits,  171. 
Fishmoth,  117. 
Fish- worm  (illus.),  55. 
Flagellum  (flagellum,  a  whip),  14. 
Flea,  122. 
Flicker,  221. 

Flies,  122 ;  development  of,  123. 
Flounders,  168. 
Fox  (illus.),  241. 
Frog,  178. 

Gammarus  (illus.),  106. 

Gallinje,  217. 

Ganglion  (ganglion,  a  swelling),  a 
swelling  of  the  nerve-cord  due 
to  the  accumulation  of  nerve- 
cells,  79. 

Ganoidea,  161. 

Garpike,  161. 

Garter-snake,  193. 

Gasteropod  (illus.),  80;  anatomy  and 
physiology,  81. 

Gastric  mill  (illus.),  107. 

Gastrula  (diminutive  of  gaster, 
stomach),  21. 

Geese,  213. 

Gelasimus  (illus.),  104. 

Gephyrean  worms  (illus.),  67. 

Gila  monster  (illus.),  193. 

Glass-snake,  191. 


254 


ANIMAL  FORMS 


Glires,  232. 

Gnat,  122. 

Gonionemua  vertens  (illus.),  34. 

Goose  barnacle  (illus.),  96. 

Gordius,  54. 

Gorilla  (illus.),  245. 

Grasshopper  (illus.),  117. 

Grebe,  209. 

Green  gland,  108. 

Grouse,  218. 

Grus  americana  (illus.),  212. 

Gull,  211. 

Habitat  (habitare,  to  dwell),  45. 

Hagfish,  157. 

Halicetus  leucocephalus  (illus.), 
220. 

Halidystus  (illus.),  39. 

Harvestman,  135. 

Hawks,  219. 

Helix  (illus.),  81. 

Heloderma  suspeclum  (illus.),  192. 

Hemiptera,  121. 

Heptacarpus  brevirosfris  (illus.), 
101. 

Hermit-crab  (illus.),  102. 

Herodines,  215. 

Herons,  215. 

Herring,  163. 

Homo  sapiens,  245. 

Honey-bee,  130. 

Hoofed  animals,  237. 

Horned  toads,  192. 

Hornet,  132. 

Horse-fly  (illus.),  119. 

Horsehair-snake,  54. 

Horseshoe-crab  (illus.),  139. 

Humming-bird  (ilhis.),  222. 

Hydra,  structure  of,  29 ;  multipli- 
cation of,  31 ;  regeneration  of, 
51. 

Hydractinia  (illns.),  36,  103. 


Hydranth,  33. 

Hydrozoa,  34 ;  regeneration  of,  51. 
Hymenoptera  (illus.),  128. 
Hystrix  cristata  (illus.),  233. 

Incubation  (incumbo,  to  rest  upon), 

207. 

Infusoria,  17. 
Insectivora,  234. 
Insects,  numbers,   114;    anatomy, 

115 ;  respiration,  117. 
Isopod  (illus.),  101. 

Jelly-fish,  of  Hydrozoa,  33 ;  of  Scy. 

phozoa,  37. 
Julus  (illus.),  112. 

Kangaroo,  232. 
Katydid,  117. 
Keyhole-limpet,  82. 
King-crab  (illus.),  139. 
Kingfisher,  221. 

Lacertilia,  185, 
Lamellibranch  (illus.),  72. 
Lamellirostres,  213. 
Lamprey  (illus.),  157. 
Lamp-shell  (illus.),  70. 
Lancelot  (illus.),  157. 
Lasso-cell,  30. 
Leeches  (illus.),  63;    haunts  and 

habits,  64. 
Lemur,  243. 
Lepas  (illus.),  99. 
Lepidoptera  (illus.),  125. 
Lepomis  megalotis  (illus.).  167. 
Leptoplana  (illus.),  45. 
Lice,  122. 
Life  histories  and  race  histories, 

27. 

Limicolae,  216. 
Limuhis polyphemus  (illus.),  139. 


INDEX 


255 


Littorina,  habits  of,  83. 

Liver-fluke,  49. 

Lizard  (illus.),  185. 

Lobster,  102. 

Locust  (illus.),  117. 

Long-horned  borer  beetle  (illus.), 

124. 

Longipennes,  211. 
Loon,  209. 

Lopliius piscatorius  (illus.),  169. 
Lophortyx  californicus  (illus.),  217. 
Lumbricus  terrestris  (illus.),  55. 
Lung-fish,  160. 
Lynx  (illus.),  241. 

Macroldella  (illus.),  63. 

Macrocheira,  222. 

Mammals,  characteristics  of,  225 ; 
anatomy,  226 ;  classification,  228. 

Man,  245. 

Many-celled  animals,  11. 

Marsupialia,  231. 

Marsupium  (marsupium,  a  purse 
or  bag),  232. 

May-fly,  118. 

Megapfera  versdbilis  (illus.),  235. 

Mesenteric  filaments,  40. 

Messmates,  defined,  48. 

Metamorphosis,  retrograde,  99 ;  in- 
complete, 126 ;  complete,  128. 

Metazoa,  defined,  11. 

Mice,  233. 

Millipeds  (illus.),  111. 

Minnow,  163. 

Mite  (illus.),  138. 

Mole,  234. 

Mollusks,  general  characters  of,  72. 

Molt,  of  Crustacea,  99,  110;  of 
birds,  202. 

Monarch  butterfly  (illus.),  125. 

Monkeys,  243. 

Morphology,  defined,  1. 


Mosquito,    122;  development    of, 
123. 

Moths  (illus.),  125. 
Mud-hen,  215. 
Mud-puppy  (illus.),  178. 
Multiplication  of  animals,  5. 
Muscle-cell  (illus.),  7. 
Muscular  system,  use  of,  4. 
Mussel,  77. 

Mysis  americana  (illus.),  100. 
Myhlus  edulis  (illus.),  77. 

Nauplius  (illus.),  99. 
Nematoda  (illus.),  52. 
Nemertean  worm  (illus.),  70. 
Nereis  (illus.),  59. 
Nerve-cell  (illus.),  7. 
Nettle-cell  (illus.),  30. 
Neuroptera,  118. 
Newt  (illus.),  178. 
Night-hawk  (illus.),  222. 
Notochord,  151. 
Nucleus  (illus.),  9. . 

Octopus punctatus  (illus.),  87. 
Oligocha?tes,  59. 

Operculum  (operculum,  a  lid),  87. 
Opossum  (illus.),  231. 
Opossum-shrimp  (illus.),  100. 
Orang-utan  (illus.),  243. 
Orb-weaving  spider,  136. 
OrnitliorhyncJius  paradoxus  (illus- 
tration), 230. 
Orthoptera,  117. 
Ostrich  (illus.),  209. 
Oyster,  77. 
Owls,  219. 

Pagurus  bernhardus  (illus.),  103. 
Paludicola?,  215. 
Pandorina  (illus.),  19. 
Panther  (illus.),  241. 


256 


ANIMAL  FORMS 


Paramcecium  (illus.),  15. 

Parapodium  (para,  alongside  of; 
pom,  foot),  60. 

Parasitism,  48. 

Passeres,  223. 

Pelican  (illus.),  212. 

Pelicanus  erythrorhynchus  (illus.), 
212. 

Perca  flavescens  (illus.),  155. 

Perch,  166. 

Perching  birds,  223. 

Peripatus  eiseni  (illus.),  111. 

Pheasant,  217. 

Physalia  (illus.),  37. 

Physiology  (physis,  the  nature  of 
a  thing ;  logos,  a  discussion),  1. 

Pici,  221. 

Piddock  (illus.),  75. 

Pigeons,  218. 

Pike  (illus.),  164. 

Pill-bug  (illus.),  105. 

Pineal  gland,  198. 

Planaria  (illus.),  45. 

Plants  and  animals,  differences  be- 
tween, 1. 

Plants,  characteristics  of  higher,  2. 

Plant-lice,  122 ;  in  ant-nests,  129. 

Plastron,  188. 

Plover,  killdee,  216. 

Polychaetes,  59;  sedentary  (illus.), 
61 ;  development  of,  63. 

Polynoe,  brevisetosa  (illus.),  61. 

Polyzoa  (illus.),  68. 

Porcellio  scaber  (illus.),  105. 

Porcupine  (illus.),  232. 

Porpoise,  234. 

Portuguese  man-of-war  (illus.),  36. 

Prairie-dog,  233. 

Prawn  (illus.),  100. 

Precocial  birds,  208. 

Primates,  243. 

Proboscis,  of  flatworms,  46. 


Procyon  lotor  (illus.),  240. 
Protoplasm  (protos,  first;  plasma, 

anything  molded),  9  ;  structure 

of,  10. 
Protozoa,    11 ;    characteristics   of, 

17;  colonial,  19. 
Pugettia  richii  (illus.),  104. 
Pulsating  vacuoles,  16,  17. 
Pygopodes,  209. 

Quail  (illus.),  217. 

Rabbit,  233. 

Raccoon  (illus.),  240. 

Race  histories  and  life  histories,  27. 

Radial  symmetry,  44. 

Rail,  215. 

Rain-crow,  220. 

Raptores,  219. 

Rat,  house-,  233  ;  wood-,  233  ; 
musk-,  233. 

Ratita?,  209. 

Rattlesnake  (illus.),  191. 

Recognition-marks,  203. 

Regeneration,  51. 

Reproduction,  sexual  and  asexual, 
5,32. 

Reptiles,  general  characteristics, 
185;  distribution,  191;  anat- 
omy, 195. 

Retrograde  metamorphosis,  99. 

Rotifer  (illus.),  66. 

Ruminant,  237. 

Sabella,  62. 

Salamander  (illus.),  176;  distribu- 
tion, 178 ;  structure  of,  179. 
Salmon,  163. 
Sand-dollar  (illus.),  142. 
Sandhopper  (illus.),  105. 
Sandpiper,  216. 
Sapsucker,  221. 


INDEX 


257 


Sarcoptes  scabei  (illus.),  138. 

Scelophorus  undulatus  (illus.),  185. 

Scorpion  (illus.),  134. 

Scyphozoa,  37 ;  development  of,  38. 

Sea-anemone,  40. 

Sea-cucumber  (illus.),  143  ;  regen- 
eration of,  145. 

Sea-lily  (illus.),  143. 

Sea-mat  (illus.), '68. 

Sea-urchin  (illus.),  141. 

Sea-squirt  (illus.),  152. 

Sedentary  life,  effect  of,  62. 

Segments,  of  worms,  55 ;  of  arthro- 
pods, 94. 

Segmented  worms,  55. 

Serpentes,  186. 

Serpent-star  (illus.),  141. 

Serphus  dilatatus  (illus.),  122. 

Serpula  (illus.),  62. 

Serpulids,  62. 

Seta,  55. 

Sexual  reproduction,  32. 

Shark  (illus.),  159. 

Shell-gland,  108. 

Shipworm,  75. 

Shrew,  234. 

Shrimp,  fairy,  94 ;  opossum  (illus.), 
100. 

Silk-moth  (illus.),  127. 

Silver-spot  butterfly  (illus.),  126. 

Simple  animals,  characteristics  of, 
18. 

Single-celled  animals,  11. 

Sinus,  blood,  78. 

Siren  (illus.),  178. 

Slug  (illus.),  80. 

Snail,  common  (illus.),  80;  arma- 
dillo (illus.),  82 ;  naked  (illus.),  82. 

Snakes,  186 ;  distribution  of,  193. 

Snipes,  216. 

Somateria  dresseri  (illus.),  214. 

Species,  origin  of,  91. 


Sperm-cell,  20. 

Sphenodon  punctatus  (illus.),  199. 

Spicule,  of  sponge  (illus.),  26;  of 
coral,  42. 

Spiders,  organization  of,  135 ;  hab- 
its, 136. 

Spinnerets,  135. 

Spiny-rayed  fishes,  166.  i 

Sponge,  development  of  (illus.), 
21;  distribution,  22;  shape  and 
structure,  23. 

Spontaneous  generation,  54. 

Springtail,  117. 

Squalus  acanthias  (illus.),  159. 

Squash-bug,  122. 

Squid  (illus.),  87. 

Squirrels,  233. 

Starfish  (illus.),  140  ;  regeneration, 
145 ;  structure,  146. 

Steganopodes,  212. 

Stickleback,  164. 

Structure  and  function,  correla- 
tion of,  6. 

Strongylocentrotus  purpuratus  (il- 
lustration), 144. 

StrutMo  camelus  (illus.),  210. 

Sturgeon  (illus.),  161. 

Sunfish  (illus.),  166. 

Symmetry,  radial  and  bilateral,  44. 

Swan  (illus.),  213. 

Swift,  222. 

Tcenia  solium  (illus.),  51. 

Tapeworm  (illus.),  50;  develop- 
ment, 51 ;  in  relation  to  regen- 
eration, 51. 

Tarantula  (illus.),  137. 

Teeth,  use  of,  2. 

Teleostei,  160. 

Termites  (illus.),  120. 

Tern,  211. 

Terrapene  Carolina  (illus.),  189, 


258 


ANIMAL  FORMS 


Thousand-legged  worms  (illus.), 
111. 

Threadworms  (illus.),  52. 

Thysanura,  117. 

Tick,  138. 

Tiger  salamander,  178. 

Toad  (illus.),  178. 

Trap-door  spider  (illus.),  137. 

Trematode  (illus.),  48 ;  develop- 
ment, 51. 

Trichina  spiralis  (illus.),  53. 

Trigger  hair,  31. 

Turkey,  218. 

Turtles,  188;  structure,  189;  dis- 
tribution. 194. 

Typhlichthys  subterraneus  (illus.), 
163. 

Ungulata,  237. 

Vacuole,  pulsating,  16 ;  use  of,  17. 
Velum  (illus.),  35. 
Vespa,  nest  of  (illus.),  131. 
Vinegar  eel  (illus.),  53. 
Volvox  (illus.),  19 ;  multiplication 

of,  20. 
Vertebrates,  characteristics  of,  145 . 

classification,  143. 


Vorticella  (illus.),  16. 

Vulpes  pennsylvanicus  (illus.),  241. 

Wasps,  128 ;  habits  of,  131. 
Water-boatman,  121. 
Water-bug  (illus.),  121. 
Water-dog  (illus.),  178. 
Water-flea,  95. 
Whale,    humpback    (illus.),    235; 

sperm,  236. 
Whale  lice,  107. 
Wheel-animalcule  (illus.),  66. 
Wheel-weaving  spiders,  136. 
Whippoorwill,  222. 
White  ant  (illus.),  120. 
Wood-beetle  (illus.),  124. 
Woodchuck,  233. 
Woodcock,  216. 
Woodpeckers,  221. 
Worms,  general  characters  of,  44 ; 

classification,  45. 

Yellowhammer,  221. 
Yellow-jacket,  132. 

Zirphcea  crispata  (illus.),  76. 
Zoology,  1. 
Zoophyte,  29. 

(1) 


THE   END 


IS'B 


Form  L-9-10w-5,'28 


•__     *     0008647677 


